The NADP-specific malate dehydrogenase isozymes were controlled by multiple gene systems. Three genes coding for dimeric enzymes segregated in a dependent fashion (NADP-Mdh ₁, NADP-Mdh ₂, NADP-Mdh ₃). A fourth gene (NADP-Mdh ₄), also coded for dimers, but was not polymorphic in B. vulgaris. A fifth gene (NADP-Me ₁) coded for enzymes active as monomers. Two genes were found to control the main zone of NAD-specific malate dehydrogenase: one coded for dimers (Mdh ₁), while a second (Mdh ₂) was not polymorphic in the assessions studied. 6-P-Gluconate dehydrogenase was not polymorphic in B. vulgaris; the two types detected on SGE₁ electrophoresis were due to developmental expression of the different systems. No genetical segregations could be detected in progeny of crosses of the distinct phenotypes. A shikimate dehydrogenase gene (Skdh ₁) that coded for monomers was identified. The diaphorase system was rather complex, but one gene (Dia ₁) coding for monomeric enzymes could be identified. Aconitase was found to be controlled by two independent genes (Aco ₁, Aco ₂), both polymorphic and coding for proteins active as monomers. Tight linkage was found between the genes NADP-Mdh ₁, NADP-Mdh ₂ and NADP-Mdh ₃. Linkage was also found between a pollen fertility restorer (Z) and the Mdh ₁ gene. The identification of linkage with Aco ₁ needs further investigation. R segregated independently from Mdh ₁, Aco ₁ and Dia ₁. Independent segregations were scored for isozyme genes Pgm ₂, Icd ₁, Ak ₁, Gpi ₁, Aco ₁ and Dia ₁.