The persistent Müllerian duct syndrome (PMDS) is characterized by the persistence of Müllerian derivatives, uterus and tubes, in otherwise normally virilized males. In a previous study, we showed that this syndrome is heterogeneous, with lack of production of anti-Müllerian hormone (AMH) by testicular tissue accounting for only some, AMH-negative, cases of this disorder. We have characterized the point mutation responsible for an AMH-negative PMDS in three siblings: a guanine to thymine transversion at position 2096 in the fifth exon changes a GAA triplet, coding for glutamic acid, to a TAA stop codon. The mutation could also be recognized, using the polymerase chain reaction, on RNA produced in trace amounts by a lymphoblastic cell line. The translation product, although undetectable in testicular tissue, could be visualized in culture medium of cells transfected with the mutant gene.