An analysis is made of the social behaviour of the male laboratory rat using the following methods. One rat is introduced into the home cage of another. One observer records the series of elements shown by each rat. These results are tabulated in sequence tables of elements. The tables are analysed by calculating an "expected" value for each cell and comparing this with the observed value. An ethogram is built up showing the relationships of the elements seen when the rats are close together and indicating the possible motivation of these elements in terms of the interaction of Aggression and Flight. It is shown that the Flight motivated elements fall into two groups, one leading to Crouch and the other leading to Submissive Posture. The occurrence of grooming and digging as displacement activities is shown and is contrasted to the occurrence of mounting which appears to be separately aroused in male-male situations. A group of elements occurring when the rats are at a distance from each other, and showing conflict between approach and avoidance, is described. It is suggested that there are two main Flight pathways, one leading to a Submissive Posture and the other to Crouch or Retreat, the occurrence of these is related to two types of behaviour seen in the wild, intra-colonial and territorial. Finally, the possible occurrence of an Approach component other than Aggression or Mating, which might be called a social drive, is suggested.