Carbamyl Phosphate Synthetase I (CPS1) (EC 6.3.4.16) is a highly conserved mitochondrial enzyme catalyzing the first committed step of waste nitrogen metabolism in the urea cycle. Using FISH for physical mapping and CEPH families for linkage analysis, we mapped the CPS1 gene (CPS1) to 2q34-->q35, reassigning it from 2p where it was originally mapped.