Screening of crude extracts of the bark of Annona bullata showed cytotoxic and pesticidal activities. By monitoring with brine-shrimp lethality, two novel, extremely potent acetogenins, bullatacin [1] and bullatacinone [2], were isolated. Spectral and chemical methods identified bullatacin as a diastereomer of asimicin. Bullatacinone represents bullatacin with the lactone cleaved and reformed at the 4-OH. Compounds 1 and 2 show selective cytotoxicities in human tumor cell lines, and certain susceptible cells give ED50 values as low as 10(-12)-10(-15) micrograms/ml. Bullatacin was pesticidal at concentrations as low as 1 ppm, but bullatacinone lacked pesticidal activities. The known compounds liriodenine and (-)-kaur-16-en-19-oic acid were also isolated and were lethal to brine shrimp but were not significantly cytotoxic.