The application of a computer-assisted structure elucidation expert system, CISOC-SES, leading to the unequivocal 1H, 13C and NOE resonance assignment of betulinic acid, a biol. active triterpenoid with complicated NMR resonances, is described. The procedure consists of peak picking that is independent of background information, systematic interpretation of connectivity information from 2D NMR into bond constraints and resonance assignment based on the proposed structure. De novo structure generation based solely on the mol. formula and spectral data is also described. This application demonstrates the potential of efficient and systematic structure elucidation of natural products with modern high-resoln. NMR spectroscopy combined with artificial intelligence. [on SciFinder (R)]