The biosynthesis and turnover of N,N-dimethyltryptamine and 5-methoxy-N,N-dimethyltryptamine have been studied in the pasture grass Phalaris tuberosa by a combination of feeding and trapping experiments using radioisotopically labelled compounds. Their turnover has been demonstrated by feeding tryptophan and tryptamine. The combined results of the feeding and trapping experiments indicate that at least five pathways could be operating in the biosynthesis of 5-methoxy-N,N-dimethyltryptamine.