Unrelated clinical episodes were observed in two separate oceanariums characterized by recurrent history and diagnostic findings and an unexplained cause. Investigations concluded that in one park, deaths occurred as a result of chlorine dioxide intoxication derived from an abnormally high utilization of chlorite as an antibacterial agent. The circumstances favoring the accumulation of chlorine dioxide are discussed. In another oceanarium, toxic hepatitis was produced in dolphins which had chronically consumed small bites of "non-toxic" paint. Environmental trouble shooting for preventive purposes is discussed.