<jats:title>Abstract</jats:title><jats:p>Two new unique cytotoxic metabolites, conicaquinones A (<jats:bold>1</jats:bold>) and B (<jats:bold>2</jats:bold>), each possessing a 1,1‐dioxo‐1,4‐thiazine ring, were isolated from the Mediterranean ascidian <jats:italic>Aplidium conicum</jats:italic>. Their structures were established by an extensive spectroscopic analysis. Compounds <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> exhibited a strong cytotoxicity in vitro against rat glioma cells. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)