The intratesticular tissue oxygen tension (= IT-pO2) depends on the testicular perfusion. Polarographic microcatheter probes have recently become available and are suitable for continuous measurements of the tissue oxygen tension. In 20 adult albino rats flexible Clark-type oxygen electrodes (1.5 F) were used for simultaneous monitoring of IT-pO2 of the ipsi- and contralateral testicle during unilateral torsion. A counterclockwise 720 degrees torsion caused a decrease of IT-pO2 from 21 mm Hg (+/- 5 mm Hg) to 5 mm Hg (+/- 1.5 mm Hg) in the twisted testicle within 5-7 min. After detorsion the IT-pO2 returned to normal level in the following 25 min. The IT-pO2 of the contralateral testicle showed no significant changes during torsion for 1 h or after detorsion. Thus, if the oxygen utilization is unchanged a unilateral acute torsion for 1 h does not cause a decrease in perfusion in the contralateral testicle. It will probably also prove possible to use oxygen tissue tension measurements to improve our understanding of testicular perfusion in humans.