The peppery nature of one of the most common edible varieties of Caulerpa racemosa var. clavifera led to the undertaking of this investigation, but the peppery principle has as yet eluded isolation. However, during the Soxhlet extraction of the powdered dry algae with ether, a new red pigment, caulerpin (C21H18N2O4), was isolated from three species of the green algal genus Caulerpa (total yield 0.63% dry wt.). Caulerpin forms red prisms from ether or acetone, m.p. 317°. On the basis of its u.v., i.r., n.m.r., and mass spectral data and chemical properties, it was assigned the structure dimethyl 6,13-dihydrodibenzo[b,i]phenazine-5,12-dicarboxylate (I).