Complementary and genomic DNA clones corresponding to human ornithine transcarbamylase (OTC) have been isolated and analyzed. Restriction fragment length polymorphisms (RFCPs) on OTC gene locus were analyzed in Japanese female population. Based on these data, a prenatal diagnosis of OTC deficiency was carried out in a risk family. A C-to-T substitution was found in exon 5 of OTC gene is an another female patient.