A questionnaire survey based on hypertension case histories was performed among a representative sample of 400 GP's and hospital doctors in Northern Ireland, Norway and Sweden, countries having markedly different utilization of antihypertensive drugs. We found a greater propensity to start antihypertensive drug treatment in Northern Ireland than in Norway and Sweden. This was true both in mild diastolic and isolated systolic hypertension. Yet the utilization of antihypertensive drugs in Sweden is about 60% higher than in Northern Ireland and 30% higher than in Norway. Swedish physicians preferred beta-blockers as their first choice to a greater extent than physicians in Northern Ireland and Norway who selected thiazides more often. In general, the choice of drugs agreed with the sales and prescribing patterns in the three countries. Besides providing more insight in therapeutic traditions the study indicates that the lower prescribing of antihypertensive drugs in Northern Ireland, and to some extent in Norway, compared to Sweden, might be due to differences in true or apparent morbidity.