Previous studies in hyperprolactinaemic women have led to conflicting views about the influence of prolactin (PRL) on serum dehydroepiandrosterone sulphate (DS) levels. This study was designed to examine the effect of a reduction of normal levels of circulating prolactin on the serum DS concentration in twenty ovulating women treated with bromocriptine for 4 months in a double-blind crossover study. The women were recruited after initial studies of hypothalamic-pituitary, gonadal and adrenal function were assessed as being normal. Blood samples were collected in the early follicular and mid-luteal phases of both placebo and bromocriptine treated cycles, and were assayed for LH, FSH, PRL, DS, oestradiol (E2), testosterone (T), androstenedione (A) and sex hormone binding globulin (SHBG). The only significant changes were in serum prolactin which decreased from a mean level of 12.6 (s.e.m. = 0.38) to 9.7 (s.e.m. = 0.36) micrograms/l (P less than 0.0025), and DS which decreased from 4.9 (s.e.m. = 0.23) to 4.5 (s.e.m. = 0.22) mumol/l (P much less than 0.0005) after treatment with bromocriptine. Although the mechanism of this phenomenon is not clear, this study suggests that PRL may have a physiological role in modulating the tonic secretion or metabolism of DS.