1. A colloidal bismuth preparation, tripotassium dicitrato-bismuthate, was given (172 mg/kg body weight, 6/7 days) to 10 laboratory rats for 14 months. Bismuth was measured by atomic absorption spectrometry in various tissues and the pattern of distribution studied. 2. Bismuth was present in kidney lung, spleen, liver, brain, heart and skeletal muscles, in descending order of abundance. Haematological data, renal and liver function tests were normal in the bismuth-treated group. 3. The data suggested that chronic ingestion of bismuth in large doses in rats results in absorption and binding to tissues. Absorbed bismuth probably crosses the blood-brain barrier.