"Introduction Concern about cancer-inducing substances has brought about many thorough studies covering the chemistry@ sources@ carcinogenicity@ and toxicological properties of PNA's. Two new factors caused the authors to prepare a current review of knowledge about PNA's. One is the application of sophisticated new diagnostic methods for detailed chemical analysis to determine individual compounds@ methods which make it possible to differentiate carcinogenic PNA's from non carcinogenic ones. The other factor is that detailed chemical analysis itself led to a better appreciation of the origin and distribution of specific hydrocarbons in the environment. Studies at the Massachusetts Institute of Technology@ Woods Hole Oceanographic Institution@ Exxon Research and Engineering Company@ and elsewhere have advanced the state of knowledge of the composition@ sources@ biological effects@ and fates of hydrocarbons in the environment. Furthermore@ recent surveys and symposia provide additional valuable material on PNA's. Examples are the extensive review by the National Academy of Sciences@ ""Particulate Polycyclic Organic Matter;"" the ""Symposium on Sources@ Effects and Sinks of Hydrocarbons in the Aquatic Environment@"" organized by the American Institute of Biological Sciences; and papers presented at the Battelle Memorial Institute in 1975 during the Symposium on Polynuclear Aromatic Hydrocarbons. Many of the basic references used herein are taken from these publications."