Yeast artificial chromosomes (YACs) of 340 and 370 kb that contain the functional human glutamate dehydrogenase gene (GLUD1) and the pseudogene GLUDP2, respectively, were isolated. These genes were not physically linked to each other nor to any other sequences homologous to the exons of GLUD1. No additional GLUD sequences were found within at least 70 kb of the 5' and 175 kb of the 3' end of GLUD1 or 150 kb of either end of GLUDP2. By in situ hybridization, GLUD1 was located at 10q23.3, GLUDP2 at 10q11.2, and another pseudogene of the GLUD gene family, GLUDP3, at 10q22.1. DNA fragments of these three genes showed cross-hybridization to the loci assigned to the other two genes, but not to any other chromosomal locus. Thus, these three genes are located at distinct positions on chromosome 10q.