The gene encoding the human G-protein-coupled inwardly rectifying potassium channel designated GIRK1 (gene symbol, KCNJ3) was mapped to chromosome 2 by analyzing its segregation in a panel of human-hamster somatic cell hybrids. This assignment was confirmed by fluorescence in situ hybridization to metaphase chromosomes, and the gene was further localized to band 2q24.1. A highly informative simple tandem repeat DNA polymorphism of the form (CA)n was identified and used to localize KCNJ3 within the genetic map of the long arm of chromosome 2.