cis-Annonacin (1) and the mixture of (2,4)-cis-and trans-isoannonacins (2 and 3), three known mono-tetrahydrofuran annonaceous acetogenins, have been isolated form the seeds of Annona cherimolia by the use of the brine shrimp lethality test (BST) for bioactivity directed fractionation. Their structures were elucidated based on spectroscopic and chemical methods. 1 showed potent cytotoxicities in the brine shrimp lethality test (BST) and among six human solid tumor cell lines with notable selectivity for the pancreatic cell line (PaCa-2) at about 1,000 times the potency of adriamycin. The mixture of 2 and 3 is over 10,000 times cytotoxic as adriamycin in the pancreatic cell line (PaCa-2). All of the compounds are about 10 to 100 times as cytotoxic as adriamycin in the prostate cell line (PC-3).