The importance of varying androgen levels for the interindividual variation in sexual activity in male rabbits was studied. Two groups of animals were used, one with a high level of precastrational activity, and the other with a low level. Following castration and injections of TP [testosterone propionate] 1 mg/day or 3 mg/day the level of performance increased beyond the precastrational level in animals with low precastrational sexual activity. The difference between the groups was also eliminated in all variables except mount frequency. The rank order of the animals according to their sexual activity was similar during all treatments, suggesting that the amount of circulating androgen is not the only determinant of the intensity of the sexual activity.