Apomorphine, which is believed to stimulate central dopamine receptors, caused a consistent increase in the ovarian weight of immature female rats treated with human chorionic gonadotrophin (HCG). This effect was blocked by haloperidol. Apomorphine also caused an acute depletion of pituitary FSH content in immature female and adult male rats. Pimozide caused a reduction in ovarian weight in HCG-treated rats in seven out of eight treatment groups in two experiments. In only one group, though, was the effect statistically significant. These findings suggest that stimulation of central dopamine receptors may excite FSH secretion. Treatment with phenoxybenzamine or inhibition of the synthesis of catecholamines by α-methyl-p-tyrosine produced variable results and raised problems of interpretation. Treatment with L-dihydroxyphenylalanine caused a consistent increase in ovarian weight in HCG-treated rats. In two experiments this increase was statistically significant, but was prevented or reduced by inhibitors of dopamine β-hydroxylas