The effect of mental arithmetic (MA) on α 2- and β 2-adrenoceptors on platelets and lymphocytes, respectively, and on plasma catecholamines was studied in normotensive (NT) and essential hypertensive (HT) subjects. There were no significant differences in responses of blood pressure, forearm blood flow (FBF) and heart rate to MA between the two groups. Baseline values and changes in adrenaline and noradrenaline levels during MA were similar in NT and HT. Alpha2-adrenoceptor density and antagonist affinity did not differ between NT and HT and was not influenced by MA. Baseline values of β 2-adrenoceptor density also did not differ between NT and HT and increased similarly after MA in both groups. Antagonist affinity to the β 2-adrenoceptors under baseline conditions was lower in HT and did not change during MA in either group. Our results indicate that there are no differences between NT and HT in α 2- and β 2-adrenoceptor density, either under baseline conditions or after mental stress.