Oxprenolol or methyldopa were administered in double-blind fashion to 29 patients shown to be persistently hypertensive. After a dose-finding, assessment, and washout period, the second drug was given. 24 patients completed a period of treatment with each drug. Blood-pressure falls were similar with each drug in the supine, standing, and post-exercise state. Half the patients responded will to low dosage (oxprenolol less than or equal to 320 mg, methyldopa less than or equal to 1 g, a day) and 9 of 11 such patients responded satisfactorily to each drug. In those whose response was inadequate, oxprenolol was increased to 960 mg or methyldopa to 3 g a day. Increasing dosage had no consistent pressure-lowering effect. Side-effects were assessed by questionnaire and no clear preference emerged. It is recommended that an inadequate response to modest dosage of either drug should lead to the use of an additional agent rather than heavier dosage.