A single-step immunoaffinity purification procedure using monoclonal antibodies was developed to isolate indole-3-acetamide from plant extracts. Antibodies from a selected clone, raised against IAA-Cl'-BSA, with pronounced ability to recognize indole-3-acetamide (IAM) were used to prepare an immunoaffinity absorbent. Antibodies purified by thiophilic interaction chromatography were immobilized on divinylsulfoneactivated agarose. This column shows a very high selectivity towards IAM compared to IAA. This single step of immunoaffinity purification gave plant extracts of sufficient purity for direct quantification by on-line spectrofluorimetry after an analytical ionsuppression-HPLC run. Successive approximation by a second analytical ion-pairing-HPLC run confirmed the validity of this analytical technique.