A double-blind study to compare the effect of 2-Br-alpha-ergocryptine (bromocriptine, CB 154, Sandoz) an ergot alkaloid with chlorotrianisene (Tace, Mer-National) on the inhibition of postpartum lactation was carried out in 38 women. At the dosages selected bromocriptine was more effective than chlorotrianisene in inhibiting lactation. Furthermore, bromocriptine significantly reduced serum prolactin levels to low normal values by the seventh day of treatment, whereas chlorotrianisene did not alter the normal progressive reduction in prolactin post-partum. Neither drug had significant toxic effects.