To improve survival following melanoma excision, wide margin resection including subcutaneous fat, is indicated. Subcutaneous fat, resected with primary melanomas, was investigated using the tyrosinase PCR method originally described for detection of melanoma cells in peripheral blood. Identification of tyrosinase transcripts was possible in 4 melanoma patients (3 Clark level IV, 1 level III), while negative results were obtained from 6 other patients (2 level IV, 3 level III and 1 level I). In control experiments, after infiltration of the reference cell line SkMel into normal fat tissue, the PCR was positive in 33% (3/9) with 10(2) infiltrated cells, 69% (9/13) with 10(4) cells and in 100% (7/7) with 10(6) cells. We conclude that detection of melanoma cells in subcutaneous fat tissue is possible by tyrosinase PCR. Follow-up studies should show whether such positive tyrosinase PCR can define patients at very high risk of tumour relapse.