The effect of administration of large amounts of zinc on immune response and serum lipoproteins was examined. Eleven healthy adult men ingested 150 mg of elemental zinc twice a day for six weeks. This was associated with a reduction in lymphocyte stimulation response to phytohemagglutinin as well as chemotaxis and phagocytosis of bacteria by polymorphonuclear leukocytes. Serum high-density lipoprotein concentration decreased significantly and low-density lipoprotein level increased slightly. The common food fad of zinc supplementation with resultant excessive intake could have deleterious effects in healthy persons.