The prognostic value of the postcoital (PC) test was studied in two groups of women in whom the infertility workup differed only in the way the PC test was timed. Fifty patients were investigated in a traditional way. In this group the PC test failed to have any substantial prognostic value. In a second group consisting of 54 patients, the PC test was timed applying ultrasonographic criteria for ovarian follicular development. This resulted in a highly significant prognostic test. Timing of the PC test by ultrasound enhanced both the reliability and the efficacy of the standard fertility investigation.