Both chronic and acute toxicity tests were performed using several species of fish. Chronic toxicity tests concerning lead were performed using mudfish (Fundulus heteroclitus). These experiments ran for 3 days. Results indicate that threshold concentration of lead for this species approaches .75 mg/1. Even at this concentration, there is definite uptake of lead at a rate greater than that exhibited in the control fish, but less than that exhibited by fish at higher concentrations. Acute toxicity tests were run using pure oxygen in an effort to determine this gas' role in the production of gas bubble disease in fish. Three fresh-water species, including the fathead minnow (Pimephales promelas), golden shiner (Notemigonus crypoleucas), and rainbow perch (Tilapea mozambique), and one salt-water species, Atlantic croaker (Micropogon undulatus), were tested. All efforts to produce gas bubble disease were futile. However, the experiments did produce serious doubt as to the role of oxygen in the production of gas bubble disease. Also, the extreme subjectiveness of the symptoms of gas bubble disease and the lack of any definitive studies of natural situations in which gas bubble disease develops (such as phytoplankton blooms) indicate that this disease and its causes are ill-defined and are in further need of clarification.