This paper deals with both the real and potential effects of metals (Selenium, Cadmium, Lead, Zinc, etc.) on the physiology of marine mammals. In particular the discussion centers around the metals acting as a "stress" factor, influencing the ability of the animals to withstand or defend against infections or diseases. I will discuss some of the clinical symptoms of poisoning by the metals, as well as long and short term storage of metals in various tissues. The problem of bioaccumlation of metals may well be a problem both in the wild and perhaps more importantly in captive animals due to food sources obtained. Representative data on both pinnipeds and cetacea will be presented. The presence of metals in subclinical amounts in the tissues of the animals may well influence the efficacy of medical treatment for ailing animals.