In anesthetized rats intravenously infused, norepinephrine (NE) was accumulated by the heart, the spleen and the lung in a dose-related manner. With the lower dose of NE (2.5 mg/kg) the organ/blood ratios were more than unity and were generally greater than with higher doses (5 and 10 mg/kg), indicating that accumulation occurred by active uptake. Nialamide and pyrogallol treatment increased accumulation in the three organs. In animals receiving nialamide and pyrogallol treatment, normetanephrine (uptake., inhibitor) and desmethylimipramine (uptake, inhibitor) inhibited accumulation in all the organs and the entire accumulation of NE could be ascribed to uptake, and uptake2 processes. In these animals, phenoxybenzamine and bilateral adrenalectomy inhibited and enhanced, respectively, the accumulation in the heart and the spleen only. NE accumulated in hearts of animals in vivo could be partly washed out by perfusion with NE-free medium in vitro. Washout was prevented by normetanephrine, indicating that this effect was not a passive diffusional leakage.