Abstract. The accuracy of identification of Serpulina hyodysenteriae strains grown in a complex medium was 90% when 2 commercial test kits were used. Unlike the other S. hyodysenteriae strains, S. hyodysenteriae strain P35/2 was unusual in being indole negative. The nonpathogenic intestinal spirochete PWS/A, which is from a different species, was indole positive and α-galactosidase negative. Identification of these spirochetes on the basis of these kits alone would have been incorrect. The analysis of volatile fatty acids by gas chromatography showed that the ratio of acetic to butyric acid was from 11:1 to 44:1 for S. hyodysenteriae strains, which distinguished them from the other spirochetes. The exception was PWS/A (acetic : butyric of 32:1), but this spirochete, unlike the S. hyodysenteriae spirochetes, also produced isobutyric acid. Short chain fatty acid (SCFA) analysis by high-performance liquid chromatography detected different SCFAs in addition to acetic and butyric acids. These additional SCFAs did not contribute to further differentiation of the porcine spirochetes.