Seminal changes following fifty-five high ligations of different sizes of varicocele have been compared with those following ligation of the spermatic vein in the absence of a varicocele. The criteria for selection of cases for operation have been discussed and it has been shown that even very small varicoceles are worthy of ligation. An Initial depression of the sperm count is generally followed by a gradual increase for as long as 15 months after operation. Depressed sperm motility associated with an adequate sperm count is a strong indication for operation but good results can also be anticipated when there is complete necrospermia. Approximately 75% of cases with low sperm counts can be expected to return to normal levels. Congenital or pathological changes in the testes[long dash]other than those produced by a varicocele[long dash]are a contra-indication to operation. In a previous communication (Scott, 1958), the results of seminal and histological studies in patients with different sizes of varicocele were presented and it was noted that all grades of varicocele appeared to play a definite part in the production of male subfertility. That particular study was undertaken to make possible the more accurate selection of cases for operation; the present study sets out to justify these criteria for elective surgery based on the seminal changes following ligation of the different sizes of varicocele.