We studied 30 spontaneous cycles, 30 cycles induced with clomiphene citrate, and 30 cycles induced with human menopausal gonadotropin-human chorionic gonadotropin to evaluate the pattern of the following parameters and their predictive value in timing ovulation: basal body temperature; cervical mucus; mean follicular diameter; serum LH and 17-beta-estradiol; and urinary LH. Compared with the spontaneous cycles, in the cycles induced with clomiphene citrate the cervical score was significantly lower on the 4 days preceding ovulation, serum LH was higher in the early follicular phase, and serum 17-beta-estradiol was significantly higher in the pharmacologically treated cycles. The highest predictive values in all groups of cycles were obtained by considering the following combinations of parameters: serum 17-beta-estradiol and LH concentrations; mean follicular diameter as shown by ultrasonography and urinary LH as determined by a rapid method.