AP appears to be safe in therapeutic doses but in large doses causes hepatic and renal necrosis in both humans and experimental animals. In animals, tissue necrosis is accompanied by depletion of GSH, and alkylation of proteins and DNA. Dose-threshold onset of both protein alkylation and tissue injury have been associated with GSH concentrations but a similar relationship with DNA binding has not been investigated. In the present study we measured DNA binding in a dose-response manner far below the GSH threshold and within the range of human therapeutic doses. Male ICR mice were treated with 10, 50, or 100 mg/kg AP (with 1-2 mCi/mouse of 3H-AP), sacrificed at 2 h, and hepatic and renal DNA was isolated by organic extraction. We added appropriate amounts of 3H-AP to proteinase-treated liver homogenates of untreated mice, isolated DNA and found no measurable radioactivity above background. In contrast, all animals treated in vivo showed 3H associated with isolated DNA (4 to 20 times 20 cpm background). Levels of binding in hepatic DNA, were (mean±SEM, n=3-7): 2.0±0.4; 6.6±2.3; and 8.1±2.7 pmol/mg DNA, respectively. In renal tissue levels of binding were 0.64+0.06, 4.14+1.33, 9.56+3.20 pmol/mg DNA, respectively. This apparent alkylation of DNA by AP reactive metabolites is observed at doses that are commonly ingested by humans and are far below those required to exceed the threshold to GSH depletion, protein alkylation, and acute cell death in this animal model. In addition to the question of initiation of neoplasia, the present data are also interesting in view of a recent epidemiological study showing a strong association between end-stage renal disease in humans and cumulative dose of AP both in daily consumption and total lifetime exposure [NEJM 331: 1675]. Supported by NIH GM44263.