Adenylosuccinate lyase (ADSL) is an essential enzyme involved in de novo purine biosynthesis. A deficiency in ADSL in humans has been shown to predispose to a neurodevelopmental syndrome with autistic features. Using both a somatic cell hybrid mapping panel and fluorescence in situ hybridization, we have precisely localized the human ADSL gene to chromosome 22q13.1-->q13.2.