Whole body autoradiographic studies performed with [3H]terbutaline after intravenous and oral administration in mice revealed that the tissue and organ radioactivity was similar to or lower than the blood radioactivity with the exception of excretory organs. This can be explained by the hydrophilic nature of terbutaline and its metabolites. However, it is noteworthy that the organ (e.g. lung and heart) concentrations of unchanged terbutaline can exceed those found in serum severalfold. This was most obvious when the drug was administered via the respiratory tract and the effect became more pronounced with time after administration. It may be explained by a more rapid clearance of drug from the blood than redistribution from tissues into the blood.