The most common causes of treatment failure in patients with malignant melanoma treated by surgical therapy alone are local or regional recurrences. These are presumed to be due to occult metastasis present at the time of the initial treatment. In an effort to control this occult regional disease, 202 patients with Stage I malignant melanoma underwent isolation-perfusion with 1-phenylalanine mustard between the years 1960 and 1970. The 2-5 and 10-year determinate survival rates were 98%, 86% and 83%, respectively. In these patients, 2% developed local recurrences, 3% developed intransit metastasis, 18% developed positive regional lymph nodes and 6% developed disseminated disease, as their first evidence of recurrence. Over 40% of these patients were benefitted by further therapy. When regional perfusion is used, the question of prophylactic lymph node dissection need not arise. There was one surgical death in this series and only a few patients had symptomatology referable to their limbs beyond 3 months.