Propranolol and other basic amines are concentrated by the lung. To test the possibility that the alveolar macrophage might participate in this process, the uptake of dl-[3H]propranolol was studied in macrophages isolated from healthy male rabbits. Uptake was time, temperature and pH dependent and was reduced in the presence of inhibitors of cellular energy metabolism, e.g., sodium azide, iodoacetate, sodium cyanide and 2,4-dinitrophenol. It was abolished by sonication of the cell suspension. Scatchard plots suggested at least 3 uptake processes, 1 of which appeared to be partition. Uptake of dl-[3H]propranolol was inhibited equally by increasing concentrations of both the dextro- and the levo-isomers and the racemate. It was also markedly inhibited by the lysomotropic agents ammonium chloride and chloroquine and by a number of tertiary amines including imipramine, chlorpromazine and methadone. Endogenous amines, including norepinephrine, epinephrine and histamine had no effect on uptake. The uptake processes in the lung for exogenous basic amines may differ from those for endogenous amines. Although uptake of endogenous amines was localized to the vascular endothelium, the lysosome may be 1 intracellular site of accumulation for exogenous amines.