By using ion exchange column chromatography with effluent monitoring using the stable, free radical .alpha.,.alpha.-diphenyl-.beta.-picrylhydrazyl as a colorimetric reagent, the occurrence of elevated levels of 5 peaks was shown in the urine of patients with metastatic disease. The tentative assignment of 2 of the peaks as dopa and 3-methoxy-4-hydroxyphenylalanine was made. Three remain unknown. The correlation of these peaks with the clinical status of melanoma patients shows that, while the individual excretion pattern of these compounds may be variable, the sustained occurrence of 1 or more of them in a patient''s urine is evidence of recurrent or continuing disease. The excretion levels appear to be proportional to the tumor burden. The results with a group of 39 melanoma patients having stage II or stage III disease indicate that this chromatography technique provides earlier evidence of liver metastases that the liver scan, may detect occult metastases generally and detected tumor in clinically enlarged lymph nodes. This method, in its present form, does not detect small pulmonary lesions earlier than chest X-ray or tomography do or brain metastases earlier than brain scan or computerized axial tomography. The technique is clinically useful for the diagnosis of melanoma patients and in their follow-up while under treatment.