Nine children with poor-prognosis malignancies--seven with advanced neuroblastoma and two with metastatic Ewing's sarcoma--were given high doses of melphalan (HDM), 150 mg/m2 (3 patients) and 180 mg/m2 (6 patients), as a 'late intensification' agent combined with noncryopreserved autologous bone marrow transplants. Melphalan levels in the plasma decreased biphasically, with mean half-lives of 6.6 min and 3.0 h. At the time of marrow reinfusion (12-21 h after HDM) the melphalan plasma level was generally below 0.1 microgram/ml. The renal contribution to melphalan clearance was low, a mean of 5.8% of the injected dose being found in patients' urine over the 12 h following HDM administration. No significant difference was seen in pharmacokinetic parameters between patients undergoing and not undergoing forced diuresis.