Genetic variants of soluble and mitochondrial malate dehydrogenase (MDH) were studied in extracts of about 4,000 placentae from the Hawaiian, Nigerian, and Swedish populations. Three new phenotypes were found. One new variant of soluble MDH was found in one individual placenta from Hawaii. In mitochondrial MDH, a new variant was found in Hawaii, and another variant was found in nothern Sweden. In addition, 2 out of 132 Nigerian placentae showed a previously described variant of mitochondrial MDH.