AbstractA soluble isocitric lyase is shown to occur in lettuce seeds. Its activity increases during germination till 72 hours and then falls again. No particulate lyase could be detected. In addition both a soluble and a particulate isocitric dehydrogenase is present in the seeds. Both enzymes react with NAD as well as with NADP. The soluble enzyme drops sharply in activity during germination, while the particulate enzyme remains at a more or less constant level of activity. By gel electrophoresis the isocitric lyase and the isocitric dehydrogenase were shown to consist of what appear to be several isozymes. The interrelation between the enzymes and their relation to fat metabolism during germination is discussed. Evidence is brought for an enzymic reaction by which isocitric acid is converted to pyruvic acid. The nature of this reaction is not clear.