We herein determined by fluorescence in situ hybridization the chromosomal localization of 2 human genes, BRAL1 and BCAN, both of which belong to the link-module superfamily, i.e. to the same band of chromosome 1q21-23. Further analysis of the genomic organization of BRAL1 and BCAN revealed that the BRAL1 gene was located 20-kb upstream of the BCAN start site. We isolated a polymorphic dinucleotide (CA) repeat sequence from a genomic clone containing the BCAN gene. High heterozygosity (0.79) makes this polymorphism a useful marker in the study of genetic disorders. Knowledge of the structure of the genes and the marker provides essential information for further analysis of the gene locus at chromosome 1q21-23.