In a retrospective study of 595 patients attending the Menstrual Disorder Clinic from January, 1978 to December, 1981, 92 patients (15.5%) had raised serum prolactin (PRL) levels (greater than 25 ng/ml) on 2 or more separate occasions with a mean (+/- S.E.M.) value of 67.1 +/- 2.5 ng/ml. Galactorrhoea was found in 27.2% of the hyperprolactinaemic patients. Primary amenorrhoea was observed in 1 patient (1.1%) with serum PRL level of 68 ng/ml. Secondary amenorrhoea of longer than 6 months' duration occurred in 61 patients (66.3%) with mean PRL level 84.2 +/- 3.3 ng/ml. The 30 patients (32.6%) with irregular menstruation had a mean PRL level of 47.2 +/- 3.3 ng/ml. Investigations revealed that 43 patients (46.7%) had idiopathic hyperprolactinaemia, 14 patients (15.4%) had drug induced hyperprolactinaemia and 1 patient (1.1%) had hypothyroidism; 18 patients (19.5%) had suspected pituitary microadenoma and 16 patients (17.2%) had abnormal radiographic findings. Bromocriptine treatment was given to 38 patients, 13 with abnormal tomographic findings (mean serum PRL greater than 100ng/ml); 18 with suspected pituitary microadenoma (mean serum PRL 94 +/- 2.7 ng/ml) and 7 with idiopathic hyperprolactinaemia (mean serum PRL 65 +/- 4.7 ng/ml). All patients (38/38) responded to treatment with restoration of menstruation and cessation of galactorrhoea within 1 to 3 months. Mean PRL level was 21.6 +/- 5.2 ng/ml at the time of response. Thirteen patients subsequently became pregnant and all delivered healthy babies.