The aim of this study was to investigate the effects of chronic, daily, 30-d administration of manganese chloride (MnCl2) to male Sprague-Dawley rats on lipid peroxidation in various tissues. Rats were intraperitoneally injected with MnCl2 (20 mg/kg) once daily for 30 consecutive days. The Mn accumulated in liver, spleen, adrenal glands, heart, kidneys, lung, and testes. This was associated with decreased lipid peroxidation in liver, spleen, and adrenal glands and a decrease in the levels of Fe in these tissues. In a second group of animals, Mn (20 mg/kg/d) and glutathione (GSH, 15 mg/kg/d) were administered ip for 30 d. GSH counteracted the Mn-induced protective fall in lipid peroxidation, but Fe levels remained lower in liver and spleen. Mn decreases lipid peroxidation in certain tissues, which may involve lowering Fe content, but interaction with Fe is not the sole mechanism.