A 483 bp Bgl II/Sal I repeat free fragment was isolated from the vector containing the human serotonin 5-HT(2B) receptor. This fragment contained part of the coding sequence located within the last exon and the entire 3'-non-translated region. It was used to probe, by Southern blots, Pst I digested DNA from a series of 20 rodent-human somatic cell hybrid lines, each of which contained different complements of human chromosomes. This 5-HT(2B) receptor probe showed hybridization to a 2-7 kb Pst I fragment which revealed 100 percent concordance with location of the gene for this 5-HT receptor variant at chromosome 2.