The major cytotoxic metabolites of Lissoclinum patella from Pohnpei have been isolated and identified. Most of the cytotoxicity is attributed to a new cyclic peptide, ulithiacyclamide B [4], which is closely related to ulithiacyclamide [1]. The proposed structure of 4 is based on spectroscopic analysis and chemical degradation. Compound 4 exhibits an IC50 of 17 ng/ml against the KB cell line but does not show selective cytotoxicity against solid tumor cells in the Corbett assay.