Transvaginal ultrasonography and daily urinary luteinizing hormone testing were used to evaluate the accuracy of urinary luteinizing hormone testing in predicting ovulation in 33 spontaneously ovulating women beginning on cycle day 10. Ovulation was confirmed in all patients with luteal phase progesterone levels and endometrial biopsy specimens. The results demonstrated that transvaginal ultrasonography and urinary luteinizing hormone testing detected ovulation in all cycles. However, the onset of urinary luteinizing hormone occurred after follicle rupture was documented by ultrasonography in 9% of the women studied. Thus the question of accuracy of urinary luteinizing hormone testing in prediction contrasted to detection of ovulation is raised. This observation is of importance in patients in whom prediction of ovulation is critical to treatment management. Therefore, an ultrasonographic examination to confirm the presence of an unruptured follicle on the day of onset of urinary luteinizing hormone surge is recommended, particularly in patients failing to conceive after three to six cycles of artificial insemination when the inseminations are timed with the onset of urinary luteinizing hormone surge.