The effects of five new mal alleles on aldehyde oxidase (AO) and xanthine dehydrogenase (XDH) activities and CRM levels in Drosophila melanogaster are described. These alleles were isolated by taking full advantage of the pleiotropic phenotype exhibited by all previously described mal alleles and represent at least three unique examples of mal function. At least one of these alleles is a representative of a new complementation group. Two other alleles exhibit a wild-type eye color in homozygous stock and one of these is "leaky", exhibiting some 50% of the XDH activity normally found in Oregon-R control flies and some 12% of the AO activity. CRM and activity levels have been quantitated for both enzymes in all allelic heterozygotes. XDH-CRM levels vary only slightly around wild-type levels while AO-CRM levels appear much more sensitive to mutational alterations.