The ability of various exteroceptive stimuli to inhibit milk ejection and the suckling-induced release of prolactin was tested in lactating rats on postpartum day 7. Milk ejection was assessed by weighing the milk in the pups’ stomachs at the conclusion of suckling; prolactin was assayed with the intradermal pigeon crop-sac method. The odor of oil of peppermint, intermittent bright light, or intermittent low intensity sounds, including personnel conversation, each significantly reduced the amount of milk obtained by the pups in 30 min of suckling following 8 hr of nonsuckling. The odor of an oily solution of chlorophyll was ineffective. The subcutaneous injection of 40 mU oxytocin concomitant with the inhibiting stimuli restored milk yields to normal values in each instance. This suggests that the stimuli employed affect milk ejection through a central inhibition of oxytocin release. The exteroceptive stimuli which inhibited milk ejection failed in the same rats to alter the extent of the reduction in the...