Amplification of the kcnk9 gene and overexpression of the encoded channel protein (TASK-3) seems to be involved in carcinogenesis. In the present work, TASK-3 expression of melanoma cells has been studied. For the investigation of TASK-3-specific immunolabelling, a monoclonal antibody has been developed and applied along with two, commercially available polyclonal antibodies targeting different epitopes of the channel protein. Both primary and metastatic melanoma cells proved to be TASK-3 positive, showing prominent intracellular TASK-3-specific labelling; mostly concentrating around or in the proximity of the nuclei. The immunoreaction was associated with the nuclear envelope, and with the processes of the cells and it was also present in the cell surface membrane. Specificity of the immunolabelling was confirmed by Western blot and transfection experiments. As TASK-3 immunopositivity of benign melanocytes could also be demonstrated, the presence or absence of TASK-3 channels cannot differentiate between malignant and non-malignant melanocytic tumours.