Succinyl CoA: 3-oxo acid CoA transferase (scot; EC 2.8.3.5) is a key enzyme for metabolism of ketone bodies. Previously, we have cloned a testis-specific succinyl CoA: 3-oxo acid CoA transferase (scot-t) cDNA from a subtracted cDNA library of mouse testis and demonstrated its expression to be specific to late haploid male germ cells. In this study, the human orthologue of mouse scot-t was cloned and characterized. The entire coding region of the mRNA and the deduced amino acid sequence of human Scot-t (h-Scot-t) showed 75.4 and 75.8% identity with mouse scot-t respectively. The mRNA was exclusively expressed in the testis, and the protein was localized to the midpiece of ejaculated spermatozoa where mitochondria exist. We showed that the h-Scot-t gene was intronless by using a polymerase chain reaction technique and that a non-functional pseudogene, 98% similar to h-Scot-t, was also located on the human genome (1p33-34.3). Furthermore, the genomic structure of the actual h-Scot-t transcription unit was found to be located in an intron (1p34.1-35.3) of the bone morphogenetic protein 8 (BMP8) gene. In conclusion, we have demonstrated that h-Scot-t is a single intronless gene specifically expressed in the testis.