This study evaluates the efficacy of a hypertension case-finding program. During office hours (8.00 am to 5.00 pm weekdays), all patients visiting a Swedish primary health care center, had their blood pressure recorded using an automatic equipment. This was made irrespective of the reason for the visit. Analysis of a record sample showed that 56 +/- 4% (95% confidence) of the 40-69 year-old fraction of the population (N = 5,806) served by the center attended the center during a two-year period. Fifty-two percent (N = 3,025) had their blood pressure checked and one percent (N = 65) fulfilled the criteria for hypertension (greater than 170/greater than 105 mmHg at three different times if aged 40-60 years; greater than 180/greater than 110 mmHg greater than 60 years). We conclude that case-finding for hypertension has low efficacy when performed in day-time primary health care.