Wide variability has been demonstrated in the properties and presumably the genetic constitution of aldehyde oxidases of 30 different strains of inbred mice. Genetic control of aldehyde oxidase (Aox) has been shown to reside in linkage group XIII and to be 9.6±0.4 recombination units from isocitric dehydrogenase (Id-1) and 28.3±3.5 recombination units from dipeptidase-1 (Dip-1). On the basis of these data and a recombination percent of 23.5±3.9 for Id-1 and Dip-1, the following gene order was deduced: Aox-Id-1-Dip-1. Furthermore, aldehyde oxidase activity was shown to be independent of adrenal influence and to have no clear-cut survival value for animals treated with large doses of N1-methylnicotinamide.