We have established nonmetastatic mouse B16 melanoma clone, C1-2, and metastatic variant, C4-1, by subcloning the 30th passage of nonmetastatic W1-4 cells. We have investigated oncogene expression and chromosomal abnormalities to see whether there is some correlation with tumor progression and phenotypic diversification in melanoma cells. Not only metastatic C4-1 but also nonmetastatic C1-2 showed similarly high expression of c-Ha-ras and c-myc oncogenes by Northern blotting method. The chromosome numbers of both clones were distributed mainly within the range of 48–52. C1-2 had about 20 biarmed chromosomes and C4-1 had 13 or 14, which made real ploidy of C1-2 and C4-1, hypotetraploidy and triploidy, respectively. 21 marker chromosomes were commonly observed, while 9 marker chromosomes peculiar to C1-2 and 4 peculiar to C4-1 were constantly recognized. In partial accordance with a previous report, chromosomes 4, 5, 6, 8, 10, 13, 18, 19, and X were additionally observed in nonmetastatic C1-2 cells, compared with metastatic C4-1 cells. Furthermore, in our study, the increase of chromosomes 1, 15, and 16 was found to be greater in metastatic C4-