The organic effects of varicocele on testicular histology were studied in bilateral testicular biopsies obtained from 30 infertile men during varicocele repair and 3 to 6 months post-operatively, using light microscopy. Before surgery and at follow-up, semen analyses were performed. The results showed a substantial improvement in semen quality in 22 cases post-operatively. Pre-operative biopsies showed depressed spermatogenesis with a predominant picture of maturation arrest, sloughing of spermatogenic epithelium, an increase in Leydig cells, thickening of tubular basement membranes and interstitial blood vessel walls with narrowing of their lumina, and increased deposition of interstitial fibrous tissue. Post-operatively, spermatogenesis improved in 22 cases, with increased mean tubular scores together with diminution in epithelial cell sloughing. The increased prominence of Leydig cells reverted to normal in 18 cases. The changes in tubular basement membranes, interstitium and interstitial blood vessels were unaffected.