Prescriptions for nitrates issued during a 6-month period in the Nottingham Health District were used to estimate the prevalence of patients thought to have angina who might potentially require specialist investigation and treatment. The 15,451 prescriptions issued were for 6856 patients. Of these, only 435 were known to hospitals. The general practitioner records of 499 patients identified from a 10% sample of general practitioners showed that in 96% the general practitioner had prescribed a nitrate for the treatment of angina. The records of five large practices with some form of diagnostic register suggested, however, that the survey detected only 73% of patients thought to have angina. With these estimates of specificity and sensitivity the prevalence of angina in Nottingham was calculated to be 1.5%. Few of the patients identified had been investigated in detail, and only 26% had attended hospital in the 3 years before the survey. There is clearly a very large potential demand for hospital resources for the investigation and treatment of angina.