Northern blot hybridization of human testicular poly (A)+ RNA to a human follicle stimulating hormone receptor probe revealed the existence of multiple mRNA transcripts. In order to investigate whether alternative splicing of the receptor occurs in the human testis we amplified the extracellular and the transmembrane domain of the human testicular follicle stimulating hormone receptor by reverse transcription polymerase chain reaction and subcloned the resulting DNA fragments. Sequence analysis of the recombinant clones revealed the existence of a truncated isoform of the human follicle stimulating hormone receptor which is spliced through a cassette exon mode without a change in the open reading frame, thereby deleting exon IX from the coding region of the receptor.