We have previously reported the isolation and structure elucidation of majusculamide C, a novel cyclic depsipeptide constituent of the deep-water variety of Lyngbya majuscula growing in the lagoon of Enewetak Atoll in the Marshall Islands, which has been shown to possess significant activity against fungal plant pathogens including Phytophthora infestans and Plasmopara viticola. Recently Kamano et al. have reported the structure of dolastatin 11, the major antineoplastic constituent of the sea hare Dolabella auricularia from the Indian Ocean, which was shown to be identical with majusculamide C except for substitution of an N-methylleucine residue in place of the N-methylisoleucine residue found in majusculamide C. This report has prompted us to recount our isolation of a trace majusculamide C homolog, 57-normajusculamide C, which we encountered in the course of characterizing a partially purified sample of majusculamide C for plant antifungal studies. Like majusculamide C, 57-normajusculamide C exhibited antimycotic activity against the indicator organism Saccharomyces pastorianus. The presence of the molecular ion at m/z 970 in the field desorption mass spectrum of 57-normajusculamide C suggested that it was a CH₂ lower homolog of majusculamide C. A comparison of the ¹H-nmr spectra of 57-normajusculamide C and majusculamide C obtained in CDCl₃ revealed that 57-normajusculamide C contains the α-hydroxyisovaleric acid residue in place of the isoleucic acid residue of majusculamide C. The amino acid sequence and the substitution of an α-hydroxyisovaleric acid unit for the isoleucic acid residue in majusculamide C were further supported by difference nOe spectroscopy and electron impact mass spectrometry (eims) of saponified 57-normajusculamide C and its permethylated derivative.