An experimental left varicocele was created in the adult rat by partial ligation of the left renal vein. A varicocele repair was performed by high ligation of the internal spermatic vein. Testicular blood flow and temperature changes were measured in control and sham animals, animals 30 days after establishment of varicocele and animals 30 days after varicocele repair. There was a statistically significant (p less than or equal to 0.01) bilateral elevation of testicular blood flow and temperature in the varicocele group compared to control and sham groups. Varicocele repair returned these blood flow and temperature values to normal. Average testicular blood flow for control, varicocele, sham varicocele and varicocele repair animals were 29.6 +/- 1, 39.8 +/- 2, 30.7 +/- 1 and 29.8 +/- 1 ml. per min. per 100 gm. tissue, respectively. Testicular temperatures averaged 34.4 +/- 0.1, 35.3 +/- 0.2, 34.4 +/- 0.1 and 34.5 +/- 0.1 degrees C, respectively. It is possible that the elevation in blood flow is associated with the elevation of intratesticular temperature, which is known to impair spermatogenesis. The data support a relationship between the varicocele and potential testicular damage.