OBJECTIVE There is a paucity of longitudinal endocrine studies of infertile patients with oligomenorrhoea. We have assessed the frequency and quality of spontaneous follicular development and luteal function in patients with oligomenorrhoea and infertility (PCOS), and have related the observed criteria to circulating LH activity. METHODS Prospective detailed investigations in a cohort of unselected patients. METHODS Infertile women with oligomenorrhoea (PCOS, n = 131) presenting to the infertility clinic at the Royal Infirmary, Glasgow. METHODS Patients were monitored with frequent plasma oestradiol (E2) concentration assessments over a minimum period of 3 weeks, starting more than 2 weeks after a menstrual bleed. When follicular maturation was identified the patient provided daily blood samples through to her ensuing menstrual bleed, and E2, progesterone, total testosterone, FSH and LH were assessed in these samples. Luteal phase progesterone profiles were assessed between the days LH surge +2 and LH surge +6 by means of a progesterone index. RESULTS Forty-eight per cent of the patients showed evidence of follicular development. The oestradiol profiles in the patients showing follicular growth were normal, but the progesterone curve was sub-normal in the early luteal phase, due to a high proportion of deficient luteal phases. The mean LH concentrations were elevated in the whole group, but no difference was observed between the mean LH values for those patients showing spontaneous follicular development and those who did not, and the incidence of ovulation was similar in the normal LH and elevated LH groups. Similarly, no relation was established between LH and the quantitative assessment of luteal phase progesterone profiles (progesterone index), and the distribution of progesterone indices was similar in the normal LH and elevated LH groups. Testosterone concentrations were positively correlated with LH (p = 0.008) but not with the incidence of spontaneous follicular growth. There was no significant difference in the incidence of spontaneous ovulation between the patients with elevated or normal mean follicular phase testosterone concentrations. CONCLUSIONS The data indicate that both LH and testosterone secretion in PCOS were closely linked, but that neither was directly linked to the incidence or inhibition of spontaneous follicular development in PCOS, or to the disturbance in luteal phase progesterone profiles.