The mouse congenital polycystic kidney (cpk) mutation causes bilateral cystic dilatation of the renal collecting tubules and leads to rapidly progressive renal insufficiency in affected homozygotes. The phenotype of the cpk/cpk mutants closely resembles that of human autosomal recessive polycystic kidney disease (ARPKD). Previously, we have reported that the cpk locus maps close to D12Nyu2 on Chromosome (Chr) 12. To determine the cpk map location more precisely, we have extended our previous studies using additional progeny and additional markers of proximal Chr 12. These recent studies position cpk within 1.3 cM of D12Nyu2, closely flanked by (Odc, D12Mit10) and (Tpo, D12Mit12). Our data support an ordered array of seven DNA markers that will provide reference points for building a physical map of the Chr 12 region centered on cpk. Moreover, these data establish that cpk lies within a linkage group that is conserved between mouse Chr 12 and human chr 2p24-2p25. This assignment to a region of homology will facilitate human linkage analyses to determine whether mouse cpk and human ARPKD are mutations of homologous genes.