The protective effect of hydroxyl radical scavengers and iron chelators has strongly implicated the hydroxyl radical in several models of tissue injury. Based on in vitro studies showing gentamicin-enhanced generation of reactive oxygen metabolites in renal cortical mitochondria, we examined the effect of hydroxyl radical scavengers and iron chelators in gentamicin-induced acute renal failure. Rats treated with gentamicin (G) alone (100 mg/kg, s.c. x 8 d) developed advanced renal failure (BUN 215 +/- 30 mg/dl) compared to saline-treated controls (BUN 16 +/- 1 mg/dl, P less than 0.001). In contrast, rats treated with gentamicin and either dimethylthiourea (DMTU, an hydroxyl radical scavenger, 125 mg/kg, i.p. twice a day) or deferoxamine (DFO, an iron chelator, 20 mg/day by osmotic pump) had significantly lower BUN (G + DMTU 48.8 +/- 8 mg/dl, P less than 0.001, n = 8; G + DFO 30 +/- 7 mg/dl, P less than 0.001, n = 8). In separate experiments, treatment with two other hydroxyl radical scavengers (dimethyl sulfoxide or sodium benzoate) and a second iron chelator (2,3,dihydroxybenzoic acid) had a similar protective effect on renal function (as measured by both BUN and creatinine). In addition, histological evidence of damage was markedly reduced by the interventional agents. Finally, concurrent treatment with DMTU prevented the gentamicin induced increase in renal cortical malondialdehyde content (G: 4.4 +/- 0.2 nmol/mg; G + DMTU: 3.1 +/- 0.2 nmol/mg, P less than 0.0001, n = 8) suggesting that the protective effect of DMTU was related to free radical mechanisms rather than to some other effect. Taken together, these data strongly support a role for hydroxyl radical or a similar oxidant in gentamicin-induced acute renal failure.