396 strains of V. parahaemolyticus, 345 originating from Togo and 51 from Japan, were submitted to the study of butandiol dehydrogenase (BDH). It was found that 52.3% of the strains were BDH-positive and 44.2% BDH-negative. An intermediate group characterized by weak reactions amounted to 3.5% of the strains. The distribution of this enzyme parallels to a certain degree the results of serotyping. Positive reactions have been found in all or most strains belonging to serotypes 03K29, O4K8, 04K12, 04K55, 05K15, and 012K19, whereas strains of serotypes 03K5 and 04K10 gave negative reactions. In serotype 05K17 both properties were found in nearly equal proportions. The test of BDH, which can supplement serotyping in characterizing strains of V. parahaemolyticus, can be applied as an aid to epidemiological studies.