Thirteen primiparous nursing mothers participated in this placebo-controlled double blind trial of metoclopramide. Therapy was started on the first postpartum day and continued for 8 days. Seven women received metoclopramide (10 mg, 3 X dd). Serum prolactin and milk yield were measured during the trial. The breast milk composition was analysed during the trial and weekly for 3 wk after the trial. A detailed analysis of the amino acid content was performed on the 6th and 21st postpartum days. During the early puerperium the total milk yield was ca. 50% greater in the metoclopramide-treated group compared to the control group. The evolution of the breast milk composition was similar for both groups, except for the amino acid content. The shift in amino acid composition occurred earlier in the treatment group indicating that metoclopramide enhances the rate of transition from colostrum to mature milk.