It has been postulated that the high malignancy of melanomas could be connected with an increased cytokeratin (CK) expression. In order to define the relationship between CK expression and genetic instability of melanoma metastases, ploidy-related parameters were compared in cytological specimens of CK-positive and CK-negative melanoma metastases. CK expression was investigated immunohistochemically in 35 melanoma liver metastases and in 52 melanoma lymphatic metastases. Ploidy-related parameters were evaluated on Feulgen-stained specimens with a CAS200 image analyzer. Cytokeratin was detected in 14 out of 35 melanoma liver metastases and in 24 out of 52 melanoma lymphatic metastases investigated. Significant differences between CK-positive and CK-negative melanoma metastases were found for the percentage of diploid cells, percentage of tetraploid cells, percentage of aneuploid cells between 4c and 8c, as well as for 5c exceeding rate. Our results confirmed that CK is present in more advanced (unstable), clearly aneuploid forms of melanoma metastases.