1. The method of dual quantification was used to study the effect of courtship of both receptive and non-receptive females on the subsequent behaviour of the male Mormoniella vitripennis. 2. The male's responsiveness to successive non-receptive females waned when the time between presentations was short. The extent of this waning was less with longer time intervals. 3. When many females were presented to a male one after another the male courted almost all of them if they were receptive females but only a few if they were non-receptive females. 4. A single courtship of either a receptive or a non-receptive female had a similar effect on the male's subsequent behaviour and recovery occurred in a similar way. 5. Courtship of 20 non-receptive females reduced the male's response to further females more than did courtship of 20 receptive females. 6. The significance of these observations is discussed with reference to the use of dummy animals and to the recent ethological concepts of reaction specific energy, motivational impulses, specific action potentiality and consummatory act. 7. An endogenous central nervous influence on the male's readiness to respond is postulated. Courtship has a short-term response-specific effect (receptive or non-receptive females) and an inhibitory stimulus-specific effect (non-receptive females). With receptive females the inhibitory effect is absent and/or mating has an excitatory effect. The stimuli provided by a receptive female must direct nervous activity rather than release a limited amount of stored energy.