We have recently described a new method for measurement of tyrosinase activity in small amounts of human serum (100 microliters), where the purification of tyrosinase is obtained by adsorption of the enzyme to concanavalin A sepharose. The method, which measures stereospecific dopa oxidation, was used in the winter of 1992-93 for the measurement of activity in serum obtained from 30 healthy subjects and from 10 patients with melanoma metastases. The serum tyrosinase values in the 30 subjects ranged from 0.1 to 1.0 nkatal/l, and the mean value and standard deviation was 0.4 +/- 0.2 nkatal/l. In the 10 patients with melanoma, the tyrosinase serum values ranged from 1.1 to 10.6 nkal/l, and the mean value was 3.1 nkatal/l.