Phosphorylase kinase is a multimeric regulatory enzyme in the glycogenolytic pathway. Interest in various types of phosphorylase kinase enzyme deficiency has focused attention on cloning and mapping the enzyme subunits. We report the mapping of the catalytic gamma subunit gene, Phkg, to mouse Chromosome (Chr) 5 near beta-glucuronidase (Gus), between alpha fetoprotein (Afp) and erythropoietin (Epo). In addition, PCR-based polymorphism assays have been developed for the human (EPO) and mouse erythropoietin genes, and a unique recombinant inbred strain distribution pattern has been defined for Epo, a distal anchor marker on mouse Chr 5.