Two isomeric linear peptides, aspergillamides A and B (1, 2), were isolated from the mycelium of a cultured marine fungus of the genus Aspergillus. The producing strain (designated CNC-120), was obtained from a saline lake sediment sample collected from Acklins Island, the Bahamas. The structures of the new peptides were elucidated using comprehensive 2D NMR methods. At 25°C, in both acetone and dimethylsulfoxide, aspergillamide A exists as a 1:1 mixture of trans- and cis-amide rotational isomers (1a and 1b). Under identical conditions, aspergillamide B is predominantly in the cis-amide form. The absolute stereochemistries of the amino acids in aspergillamide A were assigned as L by hydrolysis and comparison with commercial standards. Aspergillamide A showed modest in vitro cytotoxicity [IC50 = 16 µg/ml) toward the human colon carcinoma cell line HCT-116.