The two mouse melanoma cell lines B16-F1 and B16-G4F retain their melanogenic capacity when cultured in vitro. Melanotropic peptides such as alpha-melanocyte-stimulating hormone (alpha-MSH) induce formation and release of melanin pigment in B16-F1 cells. In contrast, B16-G4F cells do not respond to alpha-MSH. Using receptor-binding analysis and photoaffinity crosslinking we demonstrate that the lack of response of B16-G4F cells to alpha-MSH is due to the absence of functional MSH receptors from the cell surface. Northern blot analysis of receptor mRNA revealed that MSH receptor mRNA is not expressed in B16-G4F cells. These cells represent a new tool for the study of signal pathways related to the control of melanogenesis in melanoma cells.