Abstract
The response to drugs, the reaction to handling, and the breeding performance of rats bred in unisexual and in bisexual cross-fostered litters were compared. There was no significant difference in their response to drugs, although bisexually-reared animals consistently gave a more precise dose-response line to gonadotrophin. When handled unisexually-reared males defaecated more frequently and squeaked more loudly than bisexually-reared males, a difference not evident in the females. The rate of attainment of sexual maturity was similar in both rearing types but, when mated, bisexually-reared females produced larger litters.