PIP: The role of varicocele in subfertility was examined in 200 men with poor semen quality and in 87 additional men with fair to good semen quality despite varicocele. Semen quality was evaluated in terms of sperm count, sperm motility, and sperm morphology. Of the 200 men with poor sperm quality, 65% had a sperm count below 20 million/ml and 42% were in the 0-9 million/ml range. In contrast, most sperm counts in the 87 subjects with fair to good semen quality were above 40 million/ml and none was below 20 million. Ligation was not recommended for the latter group. 106 of the 200 men in the 1st group consented to ligation of the left internal spermatic vein, and the semen quality of 77 men was followed at monthly intervals for an average of 10 months. After ligation, the percentage of those with counts below 20 million/ml fell from 63.5 to 29.7, and 40.7% appeared in the above 40 million/ml category (up from 12.5%). Before ligation, 63.3% of the 77 subjects with adequate follow-up reached an acceptable motility level (120) in contrast to 7.8% in this category before operation. More than 50% of excessively subnormal motility indexes improved to a level approaching or surpassing normal, making motility the single most significant aspect of the effects of ligation on semen quality. In terms of morphology, 91% of the 200 subjects with poor semen quality showed moderate to marked stress pathology (e.g., tapering and amorphous cells and the exfoliation of immature cells of the germinal line into the ejaculate. After ligation, the percentage of men with amorphous cells fell from 78 to 44, and the percentage of those with tapering in conjunction with immature forms dropped from 65 to 28.5. The conception rate among the 68 men for whom information was available was 47.6% (32 cases). 81% and 37% of these conceptions occurred at sperm count levels below 60 and 20 million/ml, respectively. However, 29 of the 32 cases showed passable to excellent motility indexes (120-300), suggesting that motility is a more important factor in conception than sperm count. It is hypothesized that varicocele itself may not be the causative factor in disturbed spermatogenesis. Retrograde flow of blood into the left internal spermatic vein, stasis of blood in the renal vein, and the close proximity of the outflow of hormones from the adrenal cortex may create an abnormal environment around the left testis.