We studied the distribution and retention of inhaled selenious acid and selenium metal aerosols which were similar in size and chemical form to selenium aerosols that may be produced during fossil fuel combustion. Beagle dogs were given 10 to 61 micrograms Se/kg of body weight by inhalation. Aerosols generated for the inhalation exposures were also collected and instilled into the upper respiratory tracts or stomachs of additional dogs to measure systemic absorption at these sites. Selenium-75, incorporated into the aerosols, was used to determine the Se content in the whole animal, excreta, and individual tissues as a function of time. Virtually all of the inhaled selenious acid aerosol was rapidly absorbed into the blood from the lungs, gastrointestinal tract, and the nasal membranes. Selenium metal aerosols were less rapidly absorbed. Selenium that was absorbed into the blood was translocated to the liver, kidney, spleen, and heart. Selenium-75 in these organs had a biological half-life of 30 to 40 days. Approximately 50% of the deposited Se was eliminated with a biological T1/2 of 1.2 days. Urine was the major route of excretion, accounting for 70 to 80% of the excreted Se. The long-term component of the whole-body retention function for both inhaled aerosols had a half-life of about 34 days and accounted for about 20% of the initial Se dose. The data suggested that although absorption of selenious acid into blood following inhalation was more rapid than absorption of selenium metal, once absorbed the disposition of both compounds was similar.