Numerous populations in Europe, Asia, Africa, the West Indies and New Guinea, totalling 9,282 individuals, have been surveyed for the incidence of electrophoretic variants of cyto plasmic malate dehydrogenase. The presence of a fast variant in New Guinea has been confirmed and homozygotes detected for the first time. A slow variant, previously known only from a single American Negro family, has been found in 3 out of 298 Ethiopians. No variants were found in 2,618 other Africans or in any other of the populations tested.