The human homolog of the Saccharomyces cerevisiae cell division control 27 gene (CDC27) was mapped to human chromosome 17q12-q21 using a panel of human/rodent somatic cell hybrids and localized distal to the breast cancer susceptibility gene, BRCA1, using a panel of radiation hybrids. The radiation hybrid panel indicates that the most likely position of human CDC27 on human chromosomes 17 is between the marker D17S409 and the beta 3 subunit of integrin (ITGB3). Further confirmation of this localization comes from the sequence tagged site (STS) mapping of human CDC27 to the same yeast artificial chromosomes (YACs) positive for ITGB3. The estimated distance between ITGB3 and human CDC27 is less than 600 kb.