Aliphatic hydrocarbons and linear alkylbenzenes (LABs) were determined in four species of molluscs of the Central Adriatic Sea: two bivalves, Mytilus galloprovincialis, Solen vagina and two gastropods, Patella vulgata, Cassidaria echinophora. The concentrations of total aliphatic hydrocarbons determined in the mollusc samples were between 35.0 and 68.1 μg g -1 dry wt, and they may be considered within normal limits for areas reported to be mildly polluted. In P. vulgata and in C. echinophora over 70% and 50%, respectively, of the total aliphatic hydrocarbons are represented by highly branched isoprenoids (HBIs). In M. galloprovincialis 30% is made up of squalene. These hydrocarbons are usually considered of recent biogenic origin, and in particular HBIs found in P. vulgata support previous suggestions that these alkenes might be considered molecular markers of the presence of some diatom species. LAB concentrations are between 3.2 and 15.9 μg g -1 dry wt and show that all four mollusc species are contaminated by these molecular tracers of domestic wastes. Based on their composition, the LABs appear to have been recently discharged into the marine environment. The high concentration of external isomers indicates that LABs have not been biodegraded. This is probably due to the fact that the wastes were not treated or were only partially treated prior to reaching the sampling area.Oil pollution in some coastal areas of the Mediterranean Sea is considered to be serious requiring specific studies on the sources, effects, and fate of fossil fuel compounds discharged in this environment (7). Research has been carried out to understand the origins of hydrocarbons. In particular, it is of interest to know whether the fossil hydrocarbons indicative of petroleum contamination are present along with recent biogenic hydrocarbons in order to understand what role these compounds 276