Seven different human melanoma cell lines have been tested for the presence of melanoma associated antigen p97. The sensitivity of membrane immunofluorescence assays for the antigen was increased by using a mixture of antibodies to several epitopes of p97. Six of eight melanoma lines were strongly positive. Normal bone marrow was negative. When cultured p97-positive melanoma cells were added to normal marrow, the authors were able to detect 5% contamination, by fluorescence-activated cell sorting (FACS) and immunofluorescence (IF). No melanoma cells were found in one fresh and nine frozen bone marrow specimens of melanoma patients (including two with known positive marrow by routine histologic study) evaluated for autologous bone marrow transplantation after high-dose chemotherapy.