The serum protein cystic fibrosis-associated antigen (CFAG), present at elevated levels in CF homozygotes and heterozygotes, is now known to consist of two distinct but related subunits (calgranulins A (CAGA) and B (CAGB)). Both show similarity to the S100-related calcium-binding proteins. We have previously assigned CAGA to human chromosome 1q12-q21 and demonstrate here that the cDNA probe for CAGB cosegregates with it in our somatic cell hybrid panel. cDNA probes for the related genes calcyclin (CACY) and a mouse placental protein (18A2, suggested name Capl) enabled us to confirm and refine the in situ hybridization result assigning CACY to chromosome 1q21-25 and to demonstrate that both genes cosegregate with CAGA and CAGB. Capl was mapped to a region of chromosome 3 in the mouse using the BXD recombinant inbred strain mice where the p11 protein (calpactin light chain Cal1l), another S100 family member, has been localized. Cacy is shown to be within 8 kb of Capl in the mouse genome.