We prospectively studied 62 consecutive infertile men who underwent 100 intraoperative wet prep cytological examinations of testis biopsy material obtained simultaneously with permanently fixed specimens. Wet preps were performed by placing a small sample of fresh testicular tissue on a slide, adding a drop of Ringer's lactate, and compressing the specimen under a glass coverslip. Among these 100 wet preps, complete sperm with tails were identified in 62 specimens, of which 44 contained nonmotile sperm and 18 contained motile sperm. Reproductive tract obstruction was documented in 65 testes (65%) on subsequent reconstructive surgery and/or inferred from histological evaluation, including mean mature spermatid counts on the permanent sections fixed in Bouin's solution. Obstruction was absent in the remaining testes (35%). All 18 testes with motile sperm found on wet prep were obstructed. These testes were also found to have complete spermatogenesis, a category selected to include normal spermatogenesis and slight hypospermatogenesis, determined by examination of the permanently fixed sections. The finding of motile vs. nonmotile sperm on a wet prep has positive predictive values of 100% vs. 81% for the presence of reproductive tract obstruction and 94% vs. 86% for complete spermatogenesis, respectively. The presence of motile sperm in human testis biopsy specimens is a novel finding. When any complete sperm with tail is found in a testis biopsy wet prep, obstruction is likely. When motile sperm are present, obstruction is almost certain, and immediate exploration and reconstructive surgery can be justified.(ABSTRACT TRUNCATED AT 250 WORDS)