When Rhodopseudomonas gelatinosa was grown on acetate aerobically in the dark both enzymes of the glyoxylate bypass, isocitrate lyase and malate synthase, could be detected. However, under anaerobic conditions in the light only isocitrate lyase, but not malate synthase, could be found. The reactions, which bypass the malate synthase reaction are those catalyzed by alanine glyoxylate aminotransferase and the enzymes of the serine pathway. Other Rhodospirillaceae were tested for isocitrate lyase and malate synthase activity after growth with acetate; they could be divided into three groups: 1. organisms possessing both enzymes; 2. organisms containing malate synthase only; 3. R. gelatinosa containing only isocitrate lyase when grown anaerobically in the light.