High resolution color Doppler ultrasound is a noninvasive means of simultaneously imaging and evaluating the blood flow to the testes. To define the ability of color Doppler ultrasound to detect clinically evident as well as subclinical varicoceles men referred to our urology division with oligospermia and infertility underwent spermatic vein venography of the left testis if there was physical examination and/or color Doppler ultrasound evidence of a varicocele. The detection of valvular incompetence on venography was considered diagnostic for a varicocele. Of 17 study patients physical examination detected 10 of 14 venographically evident varicoceles (71%), whereas color Doppler ultrasound detected 13 of 14 (93%). Of 5 patients with a normal physical examination but with color Doppler ultrasound evidence of a varicocele 4 had a confirmatory venogram, and 1 of 2 patients with a varicocele on physical examination and a normal Doppler ultrasound had a positive venogram. These data suggest that color Doppler ultrasound of the testis may more appropriately direct further invasive testing and therapy of infertile men than physical examination alone.