Nuclear DNA profiles in primary melanomas and their metastases. DNA-aneuploid primary melanomas are said to show a greater propensity to metastasize than those without an aneuploid profile. A higher aneuploid rate has also been reported in metastatic melanomas than in primary lesions. The ploidy profile was determined of 26 primary melanomas and their first subsequent secondaries on Feulgen-stained sections from routinely processed material using a computerized video image-analysis system. In 18 of 26 cases, both primary and secondary tumor showed similar corresponding DNA patterns. These were aneuploid in 13 of 18 of the cases. A hyperdiploid pattern was present in one case in both the primary and its metastasis, and a diploid pattern was seen in four cases. There were only eight cases in which a disparity between the nuclear ploidy profile in the primary and secondary tumor was evident. Although the results suggest that ploidy studies are not useful for predicting the metastatic potential of a primary melanoma, the maintenance of similar DNA profiles in the metastases in most of these cases was interesting in regard to tumor biology. 