The effect of renal failure on melphalan pharmacology and toxicity has been poorly understood. Such information is of interest because melphalan is the most commonly used anticancer drug in the treatment of multiple myeloma, which is frequently associated with renal failure. We have studied the disposition and marrow toxicity of parenteral melphalan in dogs before and after induction of renal failure with subtotal nephrectomy. The surgical procedure decreased the creatinine clearance by an average of 62% (P = 0.001). The lowest neutrophil counts following i.v. melphalan (1 mg/kg) averaged 4.9 x 10(3)/mm3 pre-nephrectomy and 0.9 x 10(3)/mm3 post-nephrectomy, respectively (P = 0.002). The mean lowest recorded platelet counts after melphalan (1 mg/kg) were 115 x 10(3)/mm3 in the pre-nephrectomized dogs, and 9.7 x 10(3/mm3 in those who had been nephrectomized (P = 0.002). Following nephrectomy, i.v. melphalan's terminal-phase plasma half-life and renal clearance were both raised (P = 0.02) to 75% over pre-nephrectomy values. These studies show that i.v. melphalan-induced myelosuppression is markedly increased and its plasma elimination and renal clearance significantly decreased in the presence of renal dysfunction in dogs. These data suggest that parenteral melphalan's starting dose be decreased by at least 50% when used in myeloma patients with renal failure.