To determine the extent of nuclear DNA abnormalities and their relationship with prognosis of stage II malignant melanoma, metastatic melanomas in lymphadenectomy specimens of 22 patients were studied by a computerized digital imaging system. The DNA ploidy pattern was aneuploid in 86% of the cases and tetraploid in the remaining 14%. In metastatic melanomas, there was a single clone in one third of patients and multiple clones in the remaining two thirds. Poor survival rate was associated with multiple clones and greater than 30% of mean coefficient of variation of DNA content. With tumor progression stem-cell lines often became heterogeneous with the development of multiple clones and widespread DNA values. These abnormalities, determined by nuclear DNA ploidy analysis, provide useful prognostic information.