Hormone replacement studies have suggested that both prolactin and growth hormone (GH) are two components of a complex of hormones essential for the complete restoration of milk yield in the hypophysectomized lactating goat, although once restored the milk yield can be maintained for at least 3 weeks when prolactin is absent from the complex (Cowie, 1971). Furthermore, recent work, using radioimmunoassay methods, has shown that the stimulus of milking causes a considerable increase in the level of both prolactin (Bryant, Greenwood & Linzell, 1968; Johke, 1969; Hart, 1972) and GH (Hart & Flux, 1973) in the blood of the lactating goat. To investigate further the effects of the release of these hormones at milking on milk yield in the goat, three lactating British Saanen goats were daily injected subcutaneously with 1·5 ml of an increasing dose (5–20 mg/goat) of the ergot alkaloid 2-bromo-α-ergocryptine-methane-sulphonate (CB 154, kindly supplied by Sandoz Ltd,