Previous work in animal models has recapitulated and refined the clinical observation that longer periods of testicular torsion are associated within increased damage to the testis. Minimum times of damage-inducing torsion have not been established, however, nor has it been established to what degree blood flow returns to the testis on examination several hours or days after the torsion repair. Adult male rats were subjected to 0.5-h or 1.0-h 720 degrees torsion and examined for effects on testis weight, histology, and daily sperm production (DSP). None of the parameters examined were affected by 0.5-h, but all were affected by 1.0-h torsion. In a subsequent experiment, adult rats were subjected to unilateral, 1-h, 720 degrees torsion, and bilateral testicular blood flow as measured by radiolabeled microsphere distribution was determined during torsion and 4 h, 24 h, 2 days, 7 days, 15 days, and 30 days after repair of torsion. Ipsilateral testicular blood flow was reduced 94% during torsion. Blood flow was not significantly different from control or contralateral values by 4 or 24 h after repair of torsion. In spite of this return of blood flow, testis weights were significantly reduced by half by 7 days after torsion repair and spermatogenesis was clearly disrupted upon histological examination 30 days after torsion repair. Increasing the time of torsion to 2 or 4 h did not inhibit return of blood flow to the testis as measured 48 h after torsion repair. Unless the testis is infarcted, testicular blood flow in the rat model returns to normal after torsion repair.(ABSTRACT TRUNCATED AT 250 WORDS)