The human cysteine-rich protein (hCRP) is encoded by a highly conserved and widely expressed serum-inducible immediate early response gene. hCRP contains two copies of the "LIM/double zinc-finger" motif. Using a characterized hCRP cDNA probe, we demonstrate that the human CRP gene (CSRP) is present in a single copy and that both mouse and human genomes contain one or more CRP-related genes detected by hybridization at low stringency. Using a panel of human x rodent somatic cell hybrids, the hCRP locus is assigned to chromosome 1. In situ hybridization of 3H-labeled CRP cDNA to human metaphase chromosomes confirms this assignment and permits regional localization to bands 1q24-1q32. A common MspI polymorphism is identified and mapped to intron 4 of the hCRP gene. The chromosomal localization and restriction site polymorphism should prove useful in future studies of the function of this gene.