Abstract
It has been shown, using both the Lewis[forward arrow]B. N. and B. N.[forward arrow]Lewis rat strain combinations, that neonatal males are more susceptible to the induction of a high degree of immunological tolerance of skin homografts than females. Attempts to demonstrate a similar sex-effect in mice were unsuccessful. It is suggested that the significantly greater tolerance response of male rats may reflect a slower maturation of immunologic response mechanisms in this species.