The results of five broadly defined projects are reported. Cycling of xenobiotics was studied with a photo-bioassay system that used time-lapse photography to evaluate effects of Kepone and sodium pentachlorophenate on feeding activity of the lugworm, Arenicola cristata. Radio-labeled methyl parathion was used to demonstrate fate and effect in microcosms inhabited by lugworms. Uptake and depuration of chrysene by lugworms was evaluated in a flow-through system. A toxic sediment bioassay system was developed to provide a means to test effects of dredge spoil. Kepone-sorbed sediment and dredge spoil from James River and Houston Ship Channel were tested for 28 days. Long-term tests (100 days), with the same systems, were used to evaluate effects of a specific drilling mud from an active exploratory platform. Predator-prey tests of sublethal effects of xenobiotics demonstrated effect in one-prey and two-prey systems. Evaluation of sublethal effects, such as avoidance of pollution gradients, was studied in a trough-type avoidance-response system. The system recorded responses automatically and independently of an observer. Tests with pinfish demonstrated that they will avoid chlorine-produced oxidants. Usefulness of small-scale microcosms was evaluated by developing methods to culture polychaetes and crustaceans. Various aspects of the biology of selected species were studied.