SUMMARY

The follicle-stimulating hormone (FSH) content of the pituitaries of intact and ovariectomized mice of the strains C3H/Jax and ICRC, which differ in their adrenocortical responses to ovariectomy was measured at different ages. It was always higher in intact ICRC than that in intact C3H mice, particularly in younger age groups. Ovariectomy caused a fivefold increase in the FSH content in C3H mice after 1 month which was maintained up to 6 months. Thereafter there was a gradual decrease up to 12 months. The increase in pituitary FSH content in ICRC mice after ovariectomy was much less and occurred at a later age. These results agree with cytological observa-tions on the pituitaries of these two strains