Since hypertension is the foremost problem in minority and low-income populations treated in our community health centers, in 1976 we introduced a protocol that standardized diagnostic criteria and a step-care approach to the treatment of hypertension. In 1980, we modified the original protocol with guidelines for dietary management and an outline for improving physician-patient communication and health education. We hypothesized that implementing the protocol (and later modifications) would be associated with improved identification and control of hypertension. We conducted a cross-sectional study of hypertensive patients' charts in three community health centers in 1973, 1978, and 1982, and determined the status of blood pressure (BP) control of those patients by the end of the year. In 1973 (before protocol), 4 percent of hypertensives were undiagnosed and untreated, and 20 percent were lost to follow-up. Among those who remained under care, only 33 percent were under control (BP < 160/95 mm Hg). In 1978, two years after the protocol was introduced, there were fewer undiagnosed and untreated patients (2 percent), but the number lost to follow-up increased to 31 percent. The proportion of hypertensives under control increased to 70 percent. In 1982, two years after the modifications to the protocol were introduced, the proportion of patients lost to follow-up decreased to 28 percent, and the proportion of patients with controlled blood pressure increased to 79 percent. The improved level of control was statistically significant at p < .0001 (chi-square test). Although the problem of patients being lost to follow-up remains unresolved, the hypertensive patients who receive continuing treatment in our centers have a high probability of keeping their blood pressure under control. The results of this study compare favorably with those reported for groups of patients treated in other community health centers and in some private clinics.