In the acid ether-soluble fraction of methanol extracts of root nodules and roots of Alnus glutinosa (L.) Vill., indol.3yl .acetic acid (IAA) and indol-3yl-carboxylic acid (ICA) were demonstrated spectroflurometrically and the amounts determined quantitatively. Substantially more IAA was detected in nodule tissue than in roots. No seasonal variation in the IAA content, either for the roots, could be found. ICA was present in measurable amounts only in the root extracts. Biochromatographic investigations of the extracts revealed IAA to be the main auxin in the nodule tissues. These findings are discussed with special attention to results of comparable investigations of auxins in leguminous root nodules and roots.