Thirty-two patients with hypertensive disease were treated with a cardioselective blocker of beta-adrenergic receptors acebutolol ("Sectral-400", Rhone Poulenc, France). The binding of the drug and its metabolites diacetolol to plasma proteins and erythrocytes and their excretion with the saliva were studied. The significant binding of acebutolol and diacetolol to erythrocytes was shown. The ratio of the content of the free form of these substances in erythrocytes to plasma content was on the average 1.54 +/- 0.96 for diacetolol and 1.93 +/- 1.01 for acebutolol. A good correlation of acebutolol and diacetolol contents in the saliva with their contents in plasma was found. The mean values of the protein-bound fraction were for acebutolol 0.133 +/- 0.038 and for diacetolol 0.106 +/- 0.050.