Abstract
The aggressive behaviour of 26 male mice isolated for 21 days was compared with that of 26 males which were dominant in a pair for the same period. No significant difference between the two groups was found both in the latency time to attack a “standard opponent” and in the proportion of fighting/non-fighting subjects. When retested, the isolated mice showed a significant decrease in latency times. Differences in results between this study and previous experiments are discussed.