Galactorrhea is a recognized sequel of chest injury, but serum PRL levels in these patients have not been systematically documented. Therefore, we examined the PRL responses over 5 days in patients undergoing either mastectomy (10 patients) or thoracotomy (10) and in seven patients undergoing elective laparotomy (controls). Basal serum PRL levels were normal in every subject. There were no consistent or significant alterations in PRL levels after laparotomy or thoracotomy. After mastectomy, PRL levels rose from a mean preoperative level of 7.1 +/- 1.3 to 16.0 +/- 3.3 ng/ml (P < 0.01) on the first postoperative day. Mean levels continued to rise to 35.6 +/- 6.6 ng/ml (P < 0.005) on day 5; levels were supranormal in eight subjects. Hyperprolactinemia persisted in the four subjects evaluated 4 weeks postoperatively and in one of five patients evaluated at 6 months. In a retrospective study, serum PRL levels were measured months to years after thoracotomy (31 patients) and mastectomy (53 patients) and compared to levels in 41 normal female controls. Mean serum PRL levels were 8.4 +/- 1.3 ng/ml in the control group, 13.1 +/- 0.9 ng/ml in the thoracotomy group (P < 0.005), and 20.6 +/- 3.1 ng/ml in the mastectomy group (P < 0.001). One thoracotomy patient and 18 mastectomy patients (34%) had supranormal PRL levels. It is concluded that mastectomy acutely stimulates PRL secretion in most subjects, and levels may remain elevated for months, perhaps for years, in a proportion of patients. Both the acute and chronic hyperprolactinemic states are probably the result of neurogenic PRL release mediated via the suckling reflex.