Abstract An isocratic reversed-phase high-performance liquid chromatographic (HPLC) system for the separation of ( E)- and ( Z)-3-idoleacetaldoxime was developed. The indentities of the isomers were confirmed by NMR spectrometry. Both isomers could be converted into 3-indoleacetonitrile with acetic anhydride. UV irradiation of both isomers in ethanolic solution led to rapid photolysis. For the identification of the degradation products an isocratic silica gel HPLC system was developed, which showed that 3-methylindole was one major product whereas neither 3-indoleacetonitrile nor 3-indoleacetamide was formed in significant amounts. Conversely, in acetic acid both isomers were relatively stable to UV light. The implications of the results for studies of the role of 3-indoleacetaldoxime as a natural compound in higher plans are discussed.