I. This paper examines the hypothesis that the behavior a young chick shows toward a mealworm can be understood in terms of the simultaneous arousal of a tendency to approach the mealworm to peck it and a tendency to withdraw from the mealworm because of fear. 11. Three groups of 6 chicks each were observed individually between 3 and 11 days of age in three environments (home cage, and a similar cage in two unfamiliar locations) and under three states of food deprivation (0, 5, and 10 hrs) ; some of the chicks were also observed under the influence of an alcohol injection. Each experiment consisted of 4 minutes of observation with a mealworm present, preceded and followed by 2 minutes of observation with the mealworm absent. Behavior patterns of the chicks were registered on a 20-pen event recorder; frequencies and/or durations of the various behavior patterns were scored. III. Occurrence of the various activities showed no significant changes as a function of age during the course of the experiment (Fig. 2). Further, except for the first three presentations, behavior before and after the mealworm presentation showed no significant differences. The general behavior of the chicks (in the absence of the mealworm) showed marked changes as a function of environment (Figs. 3 and 4) : moving, pecking, and preening occurred less frequently with increasingly unfamiliar environments; sleeping and sitting occurred less frequently with moderate unfamiliarity, but showed a sharp increase in very unfamiliar suroundings; shrill calling occurred most frequently in moderately unfamiliar surroundings. The only activity significantly affected by food deprivation was moving (Fig. 3) : increased food deprivation resulted in increased moving. The general behavior of alcohol-injected chicks was very similar to the behavior of chicks in very un familiar surroundings. It is suggested that changes in environment are fear inducing. IV. Presentation of the mealworm allows a new behavior pattern to appear: fixating the mealworm. Fixating declined as a simple function of experience with the worm (Fig. 5) ; further, this decline was due almost entirely to shorter bouts of fixating. Fixating was a complicated function of deprivation and environment in that increasing deprivation resulted in a sharp decline of time fixating in the very unfamiliar environment, but resulted in slight increases of time fixating in the other two environments. (Fig. 6); deprivation and environmental change also interacted in their influence on bout length of fixating (Fig. 7), but only environmental change affected the number of bouts of fixating (Fig. 8). Approach to and withdrawal from the mealworm per 100 sec fixating (Fig. 9) were very highly correlated with moving in the absence of the mealworm. It is concluded that approach and withdrawal movements reflect moving that would have occurred even in the absence of the mealworm, but which is now oriented with respect to the mealworm. Further, the absolute amount of moving during fixating under each experimental condition was less than the amount of moving under that same condition when the mealworm was not present; this strongly supports the notion that the mealworm is fear inducing, and that fear of the mealworm is additive to fear of an unfamiliar environment. Approach and withdrawal per 100 sec moving (Fig. 10) were significantly correlated with bout length of fixating. Distance from the worm while fixating was slightly, but significantly, reduced with increasing deprivation (Fig. 11) ; environmental change appeared to have only an indirect effect on distance. A number of activities that occurred during, or within one second after, fixating were considered functionally irrelevant. Head shaking and sleep constituted more than 70% of all irrelevant activities. It was demonstrated that the frequency of both these behavior patterns was significantly higher in the presence of the mealworm than in its absence. The analysis of the occurrence of irrelevant sleep in the various experimental conditions gave further strong support to the notion that fear of the mealworm is additive to fear of an unfamiliar environment. The occurrence of irrelevant movements (Fig. 12) was highly correlated with bout length fixating which implicates available time as an important factor in determining their occurrence. Another important factor determining the occurrence of irrelevant activities was equilibrium fixating and other activities; equilibrium between approach and withdrawal appeared to be of no importance in the present situation. Shrill calling in the presence of the mealworm increased in some cases and decreased in other cases. Analysis of these data provided more support for the conclusions that the mealworm induces fear and that shrill calling occurs most frequently with moderate fear. V. It is suggested that the concept of ''escape'' as used by ethologists and the concept of ''fear'' as used by some American psychologists are not unitary drive systems - at least in young chicks. Rather, the term fear has been used in a restricted sense in this paper to refer to a drive system that expresses itself by progressive inhibition of general activity, by facilitation of shrill calling at moderate levels, and by facilitation of sleep at high levels. This use of the term fear is supported by the fact that fear of unfamiliar environments and fear of the mealworm are additive. Withdrawal, when it occurs, seems to be caused primarily by intense stimulation. It is suggested that fear and withdrawal are independent systems that have mutually inhibitory relations. On the other hand, fixating and fear appear to reflect a single mechanism which has much in common with the orientation reflex of Russian investigators. Since approach and withdrawal movements can be considered primarily as normally activated locomotion directed with respect to the worm, since distance from the mealworm can be adequately accounted for by the single factor of stimulus intensity, since equilibrium between approach and withdrawal movements does not lead to an increase of irrelevant movements, it is concluded that any approach-withdrawal conflict in these chicks was of secondary importance. The conflict between fixating-fear and maintenance activities is considered of primary importance. This follows first from the results for irrelevant movements, and second from the demonstration that fixating and maintenance activities have mutually inhibitory relations with each other. These results have implications for studies of drive interaction, development of behavior systems, and imprinting.