Detailed karyotypic analysis with G- and C-banding has been performed on cells of four malignant melanomas. The modal number in two cases was in the hypodiploid range, the chromosome numbers varying from 39 to 43. These two tumors had 5 to 13 marker chromosomes. The other two tumors were in the polyploid range, with modal numbers of 63 to 157 chromosomes. The cells had a minimum of 11 and a maximum of 40 marker chromosomes. Chromosome no. 1 was more frequently involved in aberrations than any other chromosome. The most common breakpoints on this chromosome were 1q21, 1q25 and 1q32. Frequent breakpoints were also noticed in the centromeric region in various chromosomes. In chromosome no. 1, however, the centromeric area does not seem to be involved. The more common breakpoints on the various chromosomes were 1q21, 1q25, 1q32, 5p13, 9q13, 11q23, 12q13. No common markers were noticed among these four cases of melanoma, but are noticed in unrelated tumors.