The administration by aerosol of fenoterol hydrobromide (Berotec) was investigated in four test persons. Two patients with operable carcinomas of the lung were given tritium-labelled fenoterol hydrobromide aerosol immediately before undergoing surgery. Parts of the pulmonary segments removed were biochemically analysed and it was observed that the radioactive contents in pulmonary tissue and blood plasma were almost identical. The pharmacokinetic data recorded after aerosol administration, viz. plasma levels and renal excretion, are not different from those recorded after oral administration. The expired air following aerosol administration was examined in two patients, whereby less than 0.1% of the dose administered was recovered. The oropharynx on the other hand, was found to contain 53% of the dose immediately after administration. Absorption via the lungs was examined in four other test persons by instilling an aqueous solution of fenoterol hydrobromide into the right bronchial tree. Comparison of renal excretion levels showed that absorption here is greater than after oral administration; the plasma level curves, however, run a very similar course.