A glycoside, which we call eryloside E(1), was isolated from the marine sponge Erylus goffrilleri and characterized by spectroscopic methods. Eryloside E possesses a rare penasterol nucleus with a t-butyl substituent on the side chain and three sugar molecules attached through carbons 3 and 30. The erylosides, which are terpene glycosides possessing either steroidal or penasterol aglycones with two or four sugar substituents, have been reported from several marine sponges.1,2 A crude extract of Erylus goffrilleri Wiedenmayer,3 1977 (Demospongiae, Choristida, Geodiidae), which was collected from Port Nelson, Rum Cay, Bahama Islands by Scuba at a depth of 120 feet on a fore reef escarpment, was shown to inhibit binding of 125[I]-Bolton Hunter labeled C5a (1-74) to its receptor. Bioassay guided fractionation of the extract led to the isolation of a series of terpene glycosides which are very weakly active in this assay. The structure of the major component of the extract was determined through spectroscopic methods. This paper will describe the isolation and structure elucidation of this metabolite, which we call eryloside E, 1.