We have studied the murine disposition and pharmacokinetics of diaziquone (AZQ), a new aziridinylbenzoquinone antitumor agent that is currently undergoing clinical trials. 14C-AZQ, dissolved in dimethylacetamide/0.01M phosphate buffer, pH 6.5, 5:95 (v/v), was administered iv to mice at a dosage of 6 mg/kg (18 mg/m2). After injection, mice were killed and plasma and organs were obtained and analyzed for total radioactivity and for chloroform-extractable 14C. Both total plasma radioactivity and chloroform-extractable plasma 14C declined very rapidly. By 3 hr, chloroform-extractable 14C was about 0.2% of its initial concentration. Within 30 min after injection, more radioactivity remained in the aqueous phase than was extracted into chloroform. When analyzed by TLC, all chloroform-extractable radioactivity in plasma as well as in brain, heart, liver, and skeletal muscle co-chromatographed with parent AZQ. Tissue distribution of 14C was extensive. 14C concentrations (dpm/g tissue wet weight) were initially greatest in heart and lung, but by 2 min after injection, were greatest in kidney, and by 10 min were second greatest in liver. Substantial amounts of total and chloroform-extractable 14C were found in brains. By 3 hr after injection, total 14C in all tissues exceeded total 14C in plasma. The apparent volume of distribution of AZQ was approximately 1 ml/g and the total body clearance of AZQ was 0.9 ml/min or 130 ml/min/m2. Extraction of tissues with chloroform showed conversion of AZQ into non-chloroform-extractable metabolites. This conversion was reproduced in vitro by mouse liver homogenate at 37 degrees C but not at 0 degree C.