Cultured cells from individuals afflicted with the genetically heterogeneous autosomal recessive disorder xeroderma pigmentosum (XP) exhibit sensitivity to UV radiation and defective nucleotide excision repair. Complementation of these mutant phenotypes after the introduction of single human chromosomes from repair-proficient cells into XP cells has provided a means of mapping the genes involved in this disease. We now report the phenotypic correction of XP cells from genetic complementation group D (XP-D) by a single human chromosome designated Tneo. Detailed molecular characterization of Tneo revealed a rearranged structure involving human chromosomes 16 and 19, including the excision repair cross-complementing 2 (ERCC2) gene from the previously described human DNA repair gene cluster at 19q13.2-q13.3. Direct transfer of a cosmid bearing the ERCC2 gene conferred UV resistance to XP-D cells.