Recurring alterations of chromosome 1 represent the most frequent site of structural chromosome abnormalities across all human solid tumors, including human cutaneous malignant melanoma. In melanoma, breakpoints involving chromosome 1 appear to accumulate most frequently at the paracentromeric regions, and secondly, to cluster within 1p36. Of interest, these three band regions (1p11-12, 1q21, and 1p36) were simultaneously recognized by a single YAC clone which was isolated from sequences mapping to 1q21. This observation indicates the common and highly conserved nature of sequences residing within these three bands. Because of this finding, we have examined the possible association of these recurring sites of rearrangements of chromosome 1 in malignant melanoma. To elucidate genomic alterations in these regions, we have analyzed melanoma samples simultaneously by fluorescence in situ hybridization (FISH) using both the YAC clone encoding 1p11, 1q21, and 1p36 homologous sequences, and an alpha-satellite probe for the chromosome 1 centromere. Twelve of 20 (60%) randomly selected melanoma cell lines showed detectable rearrangements in one or more of the chromosome 1 band regions. These results provide support for the notion that the homology between these regions is associated with chromosomal instability, and possibly, is of biologic relevance in malignant melanoma.