The data from 40 patients with essential hypertension treated with oxprenolol alone have been used to analyse the falls of blood pressure and heart rate. Blood pressure and heart rate did not fall further as the daily dose was increased above 160 mg. The range of fall in mean pressure was from 0 to 40 mmHg and there was no clear separation into response groups. Pressure falls were unrelated to sex, age, initial heart rate, increase in heart rate on standing, the fall of heart rate with the drug, or the initial height of blood pressure. In the absence of predicting factors the use of oxprenolol, and, by deduction, other beta blocking agents, in hypertension remains empirical, but the simplification of the dose range allows the response to oxprenolol to be determined quickly.