A sensitive radioimmunoassay for N,N-dimethylindolealkylamine derivatives has been developed. It is possible to detect 200 to 700 femtomoles of 5-hydroxy-N,N-dimethyltryptamine, 5-methoxy-N,N-dimethyltryptamine or N,N-dimethyltryptamine in a given sample. Antibodies were produced in rabbits immunized with a conjugate prepared by reacting 5-hydroxy-N,N-dimethyltryptamine with a diazotized dl-p-aminophenylalanine bovine serum albumin conjugate. For identification of immunoreactive material high pressure liquid chromatography was used to separate these compounds from each other and from known cross-reacting compounds found in physiological specimens. After chromatography, individual fractions were analyzed by the radioimmunoassay. This combination of high pressure liquid chromatography and radioimmunoassay has permitted the identification and quantification of these compounds in extracts of urine, plasma and whole blood from normal individuals.