The first alpha-hydroxy fatty acids from a marine sponge, namely 2-hydroxydocosanoic and 2-hydroxytricosanoic, were identified in the Caribbean sponge Amphimedon compressa. These acids were found to occur in phosphatidylethanolamine and phosphatidylserine and constituted 52% of the total fatty acid mixture of this sponge. The long chain fatty acids 5,9,23-nonacosatrienoic (29:3) and 5,9,23-tricontatrienoic (30:3), as well as a new tetratricontatetraenoic (34:4) acid, were also found in A. compressa.