Ultrasound examination and biopsy of the nonaffected testis was performed in 78 men with a unilateral testicular cancer. Each testis was measured in three planes and the volume was calculated using the formula of an ellipsoid. The ultrasonic texture of each testis was given a score ranging from 1 to 5 as follows: 1, very regular; 2, slightly irregular; 3, irregular with small echogenic points; 4, very irregular or with coarse echogenic points; and 5, irregular with demarcated areas raising suspicion of tumor. Biopsies were examined for the presence of tubules with carcinoma in situ (CIS), germinative epithelium, Sertoli cell only, and obliterations; the thickness of tubular membranes and the amount of Leydig cells were registered. The mean ultrasonic testicular volume was 12.88 ml (range 3-24 ml), which was smaller than that previously reported for normal men and larger than that previously reported for infertile men. The ultrasonic testicular volume was inversely correlated to the score. Score 4 was given to 46% of the testes (median score, 4), and the score distribution was different from that reported in normal men (median, 2) and in infertile men (median, 3). In all, 9 testes contained CIS tubules, and 8 of these were given score 4; 1 testis with CIS in only 5% of the tubules was given score 3. The predictive value of score 4 for the testis to contain CIS was 22.2%, and the predictive value of a score different from 4 that the testis would not contain CIS was 97.6%. We conclude that a large percentage of contralateral testes in men with unilateral testicular cancer have an abnormal echotexture and that CIS is most likely found in testes given score 4 by ultrasound.