For two years an office computer was used to identify patients to prompt for opportunistic screening and call for systematic screening. After the two years 92% of patients on the list had had blood pressure readings recorded within the previous five years, of which 34% resulted from special prompts and 22% from screening letters. Those who failed to respond to letters were sent questionnaires, and their records were compared with those of screened patients.With the help of a microcomputer it is practicable to sustain a continuous screening rate of between 90% and 95%.Introduction At least 7% of the population aged between 35 and 65 would benefit from a reduced blood pressure.' In 1970 Hart showed that these patients could be identified,2 and since then case finding for hypertension has been accepted in principle by most general practitioners. Audits have shown that even in well motivated practices fewer than 65% of patients have been screened in the past

In this practice, with a family practitioner committee list of 9726 patients, we use a computer register for recall, screening, morbidity data, audit, and repeat prescribing. The computing techniques used to achieve accuracy in maintaining the register are described. After one year of full use the register was validated by using the computer to select a random sample of 200 patients from patients' computer records that had not been updated recently. Two patients were untraceable, and in only 11 records were errors of information found, none of which was important. We think that it is feasible and valuable to have a household index.

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