The chemical components and the biological activity of Laurencia cartilaginea and Hypnea pannosa have been studied. Extraction and purification of H. pannosa
have resulted in the isolation of two monoterpenes identified as 3-bromo-8chloro-
6-- chloromethyl-2-methylocta-l ,6-diene (1) and 8-chloro-6--chloromethyl3- methoxy-2-methylocta-l,6-diene (2). The study of L. cartilaginea resulted in the
isolation of a sesquiterpene identified as 8-bromochamigra-1,11 (12)-diene-9-0l
(3). All the halogenated compounds showed some antibacterial properties