OBJECTIVE To evaluate the effects of a unilateral varicocele on testicular metabolism. METHODS A varicocele model was produced in ten rabbits by partially ligating the left lumbotesticular trunk (group A). Another six rabbits underwent sham operation as controls (group B). Three months later, the rabbits of group A showed a significant reduction in the bilateral testicular versus intraabdominal temperature difference, spermatozoal concentration and motility, and plasma pyruvate and lactate concentration in blood samples from both left and right testicular veins. They also showed a lesser mean percent increase of the serum testosterone level after stimulation with hCG when compared with group B. There was a significant positive correlation between the serum pyruvate and lactate levels on each side in group A. CONCLUSIONS These findings are inconsistent with the development of testicular hypoxia in the varicocelized animals, and also suggest that a left varicocele leads to a bilateral disturbance in testicular metabolism.