Using visual and radiologic lymphography, lymphatic drainage of testis, tunica vaginalis, epididymis, and vas was studied in 19 patients with inguinal hernia and epididymal cyst, and in 17 patients with idiopathic hydrocele. In the former, normal lymphatic trunks were demonstrated to lumbar nodes L1 to L4 and to iliac lymph nodes. In the hydrocele group, normal lumbar pathway was demonstrated in most cases; however, iliac route could not be shown, suggesting impairment of lymph drainage. Mean hydrocele fluid protein was found to be 5.8 gm/100 ml. Manometry of hydrocele, not previously reported, has shown that mean pressure in the hydrocele sac was 24.7 cm of fluid. Rapid reaccumulation of protein-rich fluid after tapping suggests increased capillary permeability. Possibly, a combination of impaired lymph drainage and increased capillary permeability is present in idiopathic hydrocele.