Ovarian stimulation combined with intra-uterine insemination (IUI) is an effective treatment of non-tubal infertility but most women undergo several cycles of treatment to achieve a pregnancy. This prospective study was designed to assess the consistency (or variation) of ovarian responses and the effect of various ovarian stimulation protocols on this consistency in consecutive cycles of ovarian stimulation and IUI in women with non-ovulatory infertility. A total of 86 regularly menstruating ovulating patients each completed three to six cycles of ovarian stimulation and IUI (n = 347 cycles). Ovarian stimulation was achieved by sequential clomiphene citrate/human menopausal gonadotrophin (HMG), HMG-only or combined gonadotrophin-releasing hormone analogue--HMG protocols in 33, 29 and 24 patients respectively, and each patient used the same protocol consistently throughout the study. Standard methods were used to monitor ovarian response and to perform IUI. Using each patient as her own control, repeated measurements analysis of variance revealed consistency of ovarian response in consecutive ovarian stimulation cycles, as shown by the number and mean diameter of maturing pre-ovulatory follicles, peak plasma oestradiol, duration of stimulation and mean HMG requirements. This consistency existed using any of the ovarian stimulation protocols. We conclude that regularly menstruating and ovulating women are likely to have similar ovarian responses in consecutive cycles of ovarian stimulation and IUI if the same ovarian stimulation protocol is used consistently.(ABSTRACT TRUNCATED AT 250 WORDS)