The MAGE-1 protein has been localized to the cytosol of human melanoma culture cells (MZ2-MEL.43) by subcellular fractionation. Its distribution between nuclear, mitochondrial, microsomal and cytosolic fractions was established by SDS-PAGE and immunoblotting with a rabbit antiserum and compared to that of markers for the main cell compartments. The immunoreactive material was recovered in the cytosolic fraction as a polypeptide migrating at 42 kDa, which has been further identified as the MAGE-1 protein because it comigrates with the product of cell-free transcription-translation of the MAGE-1 cDNA. Location to the cytosol was confirmed by immunofluorescence microscopy.