During the period from February to October 1983, 21 patients with malignant melanoma of the extremities were treated by hyperthermic regional isolated perfusion with L-phenylalanine mustard (melphalan). The melphalan dose for each patient was determined by the tissue volume of the perfused region, using a dose of 10 mg/l perfused tissue. Despite an average increase of melphalan dosage of 18% above the maximum for iliac perfusions recommended in the literature, no increase in toxic tissue reactions was observed after hyperthermic iliac perfusions. The same dose of 10 mg/l perfused tissue was used in hyperthermic axillary perfusions, resulting in an average decrease of melphalan dosage of 14% below the minimum recommended in the literature. By applying a constant dose per unit tissue volume, a standardization of treatment is achieved. This excludes variations like body weight, age, type of complexion, and hair color, which so far have determined dosimetry.