Four new chlorinated phenylpyrrolyloxazoles, phorbazoles A-D (1a-4) have been isolated from the sponge Phorbas aff clathrata. The structure of phorbazole A was unambiguously determined by X-ray diffraction studies of its dimethyl derivative (Ib). The structures of compounds 2-4 were determined by extensive use of 1D and 2D NMR techniques. Phorbazoles A-D represent a new class of marine alkaloids embodying the previously unprecedented, chlorinated pyrrole moiety, from marine sources.