In order to measure trace amounts of atropine in plant extracts, the radioimmunoassay technique was established.Immunogenic conjugates of haptens A (4'-carboxymethoxyatropine), B (O-succinylatropine), C (N-(carboxymethyl) noratropine) and D (N-(carboxypropyl) noratropine) with bovine serum albumin were synthesized and antisera against atropine (antisera A-D) were obtained from rabbits immunized with these conjugates.The investigation on these antisera indicated that antiserum A had the highest potency and that antiserum B had the lowest cross-reactivity among them.The assay of the atropine level in plant extracts by using antiserum A showed that this technique is much superior to gas-liquid chromatographic method used sofar.