Seventy-five male patients with arterial hypertension were exposed to psycho-emotional stress (PES). One group was investigated, using mental arithmetic exercise (MA), and the other, using a clock or compass model (C/C). The measurements were made in the absence of medication and using a 40 mg propranolol dose. The prevalent rise in arterial blood pressure, heart rate, minute volume and total peripheral resistance, associated with the MA model, is suggestive of PES-induced beta-adrenoreceptor activation. Conversely, diastolic hypertension prevailing over a moderate rise in heart rate where the C/C model was used is an evidence that there is no considerable beta-receptor activation by this test. In group 1, propranolol treatment depressed systolic, but not diastolic, arterial blood pressure, and considerably raised total peripheral resistance, whereas in group 2 both systolic and diastolic blood pressure, minute volume and total peripheral resistance declined after treatment. It is suggested that the blockade of beta-receptors has a greater hypotensive effect where those are not activated excessively, as there is no associated compensatory adjustment of the adrenoreceptor apparatus.