A new HincII polymorphism for the human serotonin 1D receptor variant (5-HT1D beta) is reported. In light of evidence indicating possible dysfunction of the 5-HT neurotransmitter system in schizophrenia, this new 5-HT receptor polymorphism was tested for linkage to schizophrenia in 5 Canadian pedigrees. Although 1 of the 5 pedigrees tested had a slightly positive lod score, there was no evidence overall for linkage to schizophrenia under dominant, recessive, or two locus models.