A single subcutaneous injection of prostaglandin F J-initiated secretion of substanti~l quantities of milk when given to non-pregnant ewes with mammary glands developed by prior treatment with ovarian steroids. A dramatic but transient increase in the levels of prolactin and growth hormone in plasma was observed. Ewes injected with ergocryptine 24 h before injection of prostaglandin F2" produced lower, but not significantly lower, yields of milk, even though the levels of prolactin in plasma were reduced to negligible values, whereas there wai'> no effect on the increase in levels of growth hormone. Control ewes not injected with prostaglandin F~<, secreted only trivial volumes of milk, with levels of pr0lactin and growth hormone in plasma remaining low.

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