1. Erythrocyte catechol-O-methyltransferase was studied in a population sample of 147 subjects.
2. There was a wide interindividual variability of catechol-O-methyltransferase activity, which was not unimodally distributed. Catechol-O-methyltransferase activity was not influenced by blood pressure, age or sex, nor was it related to plasma noradrenaline or urinary catecholamines or metanephrines.
3. It is not likely that inactivation of noradrenaline by O-methylation at least by erythrocytes is an important mechanism determining plasma noradrenaline, let alone arterial pressure.