Sequential flow cytometry was performed on 73 metastatic malignant melanomas, derived from 804 primary tumors. Tumor thickness was confirmed an excellent prognostic parameter in primary melanoma, but did not allow reliable predictions in metastatic disease. Also, aneuploidy and genetic heterogeneity, both common in metastatic melanoma, were equally distributed among patients differing in survival time. However, a remarkable acceleration was observed in the generation of abnormal cell lines in patients dying early of metastatic disease.