There is continuing uncertainty about whether morbidity and mortality of treated hypertensive patients depends on the drug(s) used to treat or only on the level of blood pressure achieved. This study was undertaken in a sample of special Veterans Administration hypertension clinics to determine which antihypertensive drugs were selected by the involved healthcare providers and how effective they were in achieving normotension. Hypertensive veterans (n = 6100) were followed in six VA Hypertension Screening and Treatment Program clinics for 46 months beginning in May 1989. Their average age was 60.7 years; 53% lived in the Stroke Belt; 46% had target organ damage, 36% were black, 23% smoked, and 10% had diabetes mellitus. Antihypertensive regimens were divided into 12 all-inclusive categories. Blood pressures were averaged at the last study visit for all patients on a regimen. The regimens of diuretic or diuretic plus beta-blocker gave the lowest average pressures (140.6/82.3 mm Hg) and calcium antagonist the highest (149.0/86.5 mm Hg). ANOVA indicated that differences between seven common regimens and also between the four single drug regimens were highly significant (P<.0001). This pattern of low treated pressure with the "old" agents and higher treated pressure with newer agents was reflected in the percentage of patients controlled below 140/90 mm Hg and the percentage uncontrolled above 159/94 mm Hg. Blacks and patients with target organ damage resembled the entire cohort in average treated diastolic blood pressure, but the former had lower and the latter had higher treated systolic blood pressure than the entire cohort.