The amino acid sequence of human prostate-specific antigen (APS) suggests that it is a member of the glandular kallikrein subfamily of serine proteases. In the mouse, the kallikrein* like family is localized in a single locus on chromosome 7. While other serine proteases are distributed over a variety of different chromosomes. To investigate the physical relationship between the human kallikrein genes, we have used in situ hybridization and Southern analysis of a human x mouse somatic cell hybrid panel to map the APS gene to 19q 13, concordant with the renal kallikrein KLKI gene. This finding indicates that APS is a member of a human kallikrein-like gene family with analogous organization to that of the mouse.