Fifty seven male patients either complaining of poor sexual development, gynecomastia or dwarfism and signs of sexual infantilism were studied. Plasma prolactin (PRL) and testosterone (T) were estimated in all patients while 33 of them were also subjected to full pituitary function tests. Twelve of the latter had an elevated basal plasma cortisol or growth hormone which suggested the patient may have been "stressed"; the results were analyzed both excluding and including these patients. The remaining patients were divided into those with a plasma T less than 8.0 nmol/l (Group A, 25 patients) and those with a plasma T greater than 8.0 nmol/l (Group B, 20 patients). The results were compared with those from 18 normal men (Group C). The mean plasma PRL in group A (108.1 mU/l) was significantly lower than that in group B (181.5 mU/l, p less than 0.005) or group C (255.7 mU/l, p less than 0.001). The difference between groups A and B became much less (p less than 0.01) when results from the "stressed" patients were included but this did not affect the difference with group C. The mean plasma PRL in group B was also significantly lower (p less than 0.05) than that in group C but the significance of the difference disappeared when all the patients were included (p less than 0.2). In the patients there was a significant correlation between plasma and PRL plasma T (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)