There is little information about the action of ergot derivatives other than bromocriptine (CB 154) on plasma prolactin and milk secretion in human beings. In a recent report it has been suggested that ergonovine might interfere with lactation when administered post partum. The present study shows that methyl-ergonovine (Methergine), a closely related compound, has no action on prolactin or milk secretion as measured in a group of 10 breast feeding mothers in comparison with another 10 untreated puerperas.