Increased responses of plasma insulin and endorphins to the oral glucose tolerance test (oGTT) have earlier been found in obese women. We studied responses of immunoreactive beta-endorphin (ir beta-E) and insulin in plasma to the oGTT in 8 non-obese women with polycystic ovaries (PCO) and in 10 healthy women. An additional control group consisted of 5 healthy women who were fasting during the study period. In the PCO group the insulin and glucose responses to the oGTT were increased, and an increase of ir beta-E from 5.9 +/- 1.5 to 8.6 +/- 2.8 pmol/l was found during the 1st half-hour period of the oGTT. In contrast, no significant change was found during the oGTT in healthy women (3.2 +/- 0.5 and 2.7 +/- 0.65 pmol/l, respectively), and in the fasting control women the mean ir beta-E level (+/- SE) decreased, from 4.5 +/- 1.2 to 3.6 +/- 1.1 pmol/l. These findings revealed increased responses of both plasma ir beta-E and insulin to the oGTT in non-obese women with PCO but their possible causal relationship remained unsolved.