Urinary melanogens are indolic and phenolic compounds which are excreted in an elevated amount in the urine of melanoma patients. Urinary melanogens can be divided into two principal groups according to their behavior during Thormählen test--Thormählen positive melanogens (TPM) and Thormählen negative melanogens (TNM). When comparing TPM and TNM (represented by homovanillic and vanillactic acids) urinary excretion in stage III of melanoma patients we have found two significantly different relations for melanogens excretion, i. e. predominating TPM urinary excretion in melanotic forms of melanomas and predominating homovanillic acid and vanillactic acid urinary excretion in amelanotic forms of melanomas. We assumed that it could be an indirect evidence of the different catalytic activity of either cresolase or catecholase activities of tyrosinase.