Assmcr.-The MeOH extract of the demospongia Cinacbyra tamtina was shown to contain, in addition to three common 3~-hydroxysterols and three cholest-4-en-3-ones, two steroids: cholest-4-ene-3,6-dione Ell and (24R)-24-ethylcholest-4-ene-3,6dione 121, which have not been previously found as naturally occurring compounds. The structures of 1 and 2 have been elucidated by spectroscopic analyses ('H and 13C-nmr, uv, ir) and confirmed via synthesis. Marine sponges are a rich source of unusual sterols, including the cholest-4en-3-ones that were first encountered in the sponge Stelleta ckzrella (1). These sterols have been isolated from sponges occurring in several parts of the world; sometimes the enone function is further conjugated with additional carbon-carbon and carbon-oxygen double bonds as in cholesta-4,7,22-triene-3,6-dione, 24methylcholesta-4,7,22-triene-3 ,6dione, and 24-ethylcholesta-4,7,22-triene-3,6dione, which are present in the sponge Rapbidostila incisa (2); 24-methylcholesta4,24(28)-diene-3,6-dione and cholesta4,22-diene-3,6-dione, present in the sponge Antboarcuata g~acea (3); and (22E>cholesta-4,6,8( 14), 22- tetraen- 3one recently isolated from the sponge Dirtyonella incisa (4). As part of our continuing research on the metabolites from Mediterranean organisms, we examined the steroid fraction of the demospongia Ciwbyra tarentitza (Pulitzer-Finali) (Porifera). This sponge has a hemispherical shape more or less flattened with a wide base of attachment; the color in life is light yellowish brown, and the consistency, in spite of the strong radiating bundles of oxeas, is weak (5). This study led to the identification of three common 3P-hydroxysterols [cholesterol, 24-methylcholesta-5-22-dien3p-01, and 24-methylcholesta-5-24(28> dien-3P-011, three cholest-4-en-3-ones Echolest-4-en- 3 -one, 24-methylcholesta4,24(28)-dien-3-one, and 24-methylcholesta-4,22-dien-3-o1ie], and two cholest-4-ene-3,6-diones, 1 and 2. Compounds 1 and 2 until now have not been reported as naturally occurring compounds.