Ricinine, isolated fromRicinuscommunisL. fed aspartic acid-3-14C and aspartic acid-4-14C, was degraded, and in each case the activity of all the carbon atoms was determined. The results obtained indicate that aspartic acid is incorporated into ricinine via the Krebs tricarboxylic acid cycle rather than directly as aspartic acid. Experiments with aspartic acid-13N support this suggestion; they indicate that the ring nitrogen from ricinine is not derived directly from the nitrogen of aspartic acid, since both it and the nitrile nitrogen contain essentially the same abundance of15N.