Contralateral testicular perfusion during unilateral testicular torsion was evaluated using simultaneous blood flow and O-2 content determinations. Two groups, each consisting of 7 rats, were studied. Sham operation or 720 degrees clockwise twisting was performed on the left testes, and blood flow, O-2 content and temperatures were monitored in the right testes for 180 min. An ultrasonic perivascular Doppler flowmeter system, an electronic thermometer and an O-2 electrode were used for the monitoring. The contralateral testicular blood flow and relative O-2 contents were stable in the control group. However, the initial and 180 min blood flow values decreased from 0.21 +/- 0.04 to 0.11 +/- 0.02 ml/min (p < 0.001), and the O-2 contents from 0.857 +/- 0.123 to 0.319 +/- 0.037 (1.0 corresponds to 19.6 mm Hg PO2, P < 0.05) in the experimental group. Unilateral testicular torsion decreases the blood flow and O-2 content of the contralateral testis. The contralateral testicular injury encountered following unilateral testicular torsion might result from hypoxia following the decrease in blood flow.