Red algae of the Laurencia genus contain a wide range of unusual secondary metabolites, many of which are halogenated. In this study the extracts of two local New Zealand species, Laurencia thyrsifera and Laurencia distichophylla have been examined in detail resulting in the isolation of several compounds some of which were previously undiscovered. Laurencia thyrsifera was found to contain a range of acetylenic cyclic ethers: the isomeric dials (82a) and (82b), which were isolated as the diacetate derivatives, the mono-acetate isomeric mixture (87a-d), the isomeric diacetates (82c) and (82d), the isomeric enones (89a) and (89b), the diene (92) and finally the bromo compound (95). The structures and stereochemistries of these compounds were established by a combination of spectroscopic and chemical techniques. A g.l.c. survey of the fatty acid components of this alga was also performed. The components of the extracts of Laurencia distichophylla were found to be metabolites of the cuparene-type. Two distinct chemo-types of Laurencia distichophylla were found to exist. The first contained the new compound (101), ebromoisolaurinterol (21), debromoaplysin (7), α-bromocuparene (13) and a polar non-halogenated compound (24). The second chemo-type of Laurencia distichophylla contained principally allolaurinterol (17) and isolaurinterol (11). Cholesterol (88) was a component of both species of algae. An extensive literature survey resulted in the collation of structural information of all the acetylenic cyclic ethers isolated from Laurencia species. Examination of the stereochemistry of these compounds permitted the proposal of a biogenetic sequence.