Especially because of their physico-chemical properties, and in particular of their lipo-solubility, it was interesting to compare the tissue distribution of two beta 2 sympathomimetics: the clenbuterol and the salbutamol. The study was realised after a direct intravenous administration of clenbuterol chlorhydrate (5 micrograms/kg) and one of salbutamol sulfate (50 micrograms/kg) given to a dog. In a first time, the determination by mass-spectrometry of the two drugs in the plasma allows the pharmacokinetic study in dogs. After a three days wash out, this same experience was repeated. The animals are sacrificed and the assays of the two beta 2 sympathomimetics were effected in lung, bronchial, muscle, heart and brain tissue samples. The tissue distribution was different for clenbuterol and salbutamol and had to be considered as factors of selectivity in the sympathomimetic beta 2 activity. Nervous central diffusion of clenbuterol is higher than salbutamol but cardiac distribution is very important for salbutamol.