The effect of prostaglandin E2 (PGE2) (3 mg/day orally for four days) on puerperal breast discomfort and prolactin secretion was investigated in eight women in a double-blind, placebo-controlled study. Scoring systems were used for daily assessment of the degree of breast discomfort. PGE2 had no effect on breast lactation, breast swelling or pain. No difference was seen between serum prolactin in the placebo- and PGE2-treated women. Contrary to a previous report, in our experimental design PGE2 had no effect on puerperal breast lactation, swelling or pain or on serum prolactin.