Manganese is an essential metal of toxicologic concern primarily because of exposure via inhalation. Environmental forms of Mn exist mainly as insoluble oxides, yet much of the research information available relates to the soluble salts. In the present study, adult male Sprague‐Dawley rats were intratracheally instilled with either soluble MnCI2or insoluble Mn3O4labeled with54Mn. Lungs and other major organs were sampled over a span of 3 mo after dosing with the respective chemicals, which were equivalent to 8 μ‐Ci and 1 μmol of manganese in 0.2 ml of buffer. There was rapid clearance of Mn from the lungs in the case of both chemicals; the chloride cleared at an initial rate of nearly four times that of the oxide. Despite this early difference, the amount of54Mn remaining in the lungs after 2 wk was similar for both compounds. The level of54Mn in the liver, kidney, spleen, and testes peaked at the 3‐d sampling point in the case of the oxide, whereas the chloride peaked in these organs within 4 h. At 1 wk after administration, however, the54Mn activity was comparable for both compounds in most organs sampled. Mn uptake in the brain was also more rapid with the chloride form, but both compounds remained at high levels for several weeks.