Pulsatile secretion of LH, FSH, PRL, oestradiol and oestrone was studied in a group of 16 patients with micropolycystic ovary syndrome (PCOS) and compared with that of normal ovulatory women in the fifth to sixth day of the cycle. Hormone concentrations were measured at 10 min intervals for 8 h starting at 0930 h. In seven subjects, the study was prolonged for 24 h, with 20 min interval samples, in an attempt to evaluate the circadian rhythm of LH by cosinor analysis. Significant fluctuations occurred in the concentration of each hormone. Values shown are mean +/- SD. PCOS subjects had high LH mean values (27.9 +/- 5.9 IU/l) (P less than 0.005). LH pulse amplitude was higher than controls (11.6 +/- 3.7 IU/l versus 5.2 +/- 1.8 IU/l; P less than 0.005) while no consistent changes in frequency or interpulse interval (62.0 +/- 10.7 min versus 65.8 +/- 19.2 min; P = NS) were found. A mean of 4.8 +/- 1.2 pulses of FSH occurred in 8 h and the mean pulse amplitude was 2.68 +/- 1.11 with no differences from controls. All patients were normoprolactinaemic. A mean of 5.5 +/- 1.9 pulses occurred in 8 h, the interpulse interval was 76.1 +/- 14.4 min and the amplitude was 2.87 +/- 0.76 ng/ml and there were no significant differences from controls; 75% of PRL pulses showed a temporal relationship with LH pulses. Oestrone mean basal values were higher in PCOS (47.2 +/- 12.5 pg/ml) than controls (32.0 +/- 9.9 pg/ml; P less than 0.02), while no differences were observed as regards oestradiol. Oestradiol pulse amplitude was nearly the same as oestrone (43.6 +/- 18.8 pg/ml and 37.7 +/- 16.1 pg/ml, respectively); 6.0 +/- 2.2 pulses and 6.0 +/- 1.6 pulses occurred in 8 h with an interpulse interval of 81.1 +/- 27.1 min and 71.8 +/- 11.1 min, respectively. Sixty-five per cent of LH pulses were followed by an oestradiol and oestrone peak. The mean time of the appearance was 17 +/- 15 min and 25 +/- 23 min, respectively. In the PCOS group a consistent 24 h rhythm in mean plasma LH levels was found with the highest hormone values at 1720 h (P less than 0.05) unrelated to apparent sleep and different from that of adult women. Pulse frequency showed a significant slowing during the night with the longest interpulse interval at 0327 h (P less than 0.03) while no significant periodicity was observed in LH pulse amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)