Respiratory function (V.E.M.S.-C.V.) and cardiovascular function (pulse and blood pressure) were studied in 5 asthmatic patients who were given isoprenaline aerosols after I.V. injection of normal saline solution (in the first step) and acebutolol (in the second step). The respiratory function is not disturbed by acebutolol. On the other hand, the cardio-accelerating effect of isoprenaline was not neutralized by acebutolol during these two assays, but significantly reduced.