Neanthes arenaceodentata has been used frequently in saltwater toxicity tests. A flowing-water system is described for the laboratory culturing of this polychaete. The system features the shallow, flat trays that are commonly used to culture shellfish. Three diet studies were conducted to determine the best diet to feed laboratory cultures to promote good growth (measured by dry weight) and survival. First, all diets (including commercially prepared diets, yeasts, whole-grain and grain by-products, algae, and animal tissue) were evaluated singly in a 28-d test. Then, selected diets, alone and in combination, were evaluated in two tests (34 and 70 d) that simulated our culture conditions. In the first test, a commercially prepared diet, prawn flakes, produced the best growth; however, worms fed macroalgae had better survival.