The most recent JNC-V guidelines for hypertension treatment call for control of blood pressure (BP) to < 140/90 mm Hg, with increased emphasis on control of systolic pressure. To determine the extent and determinants of BP control in a large multi-ethnic, low-income clinic population of diagnosed hypertensives immediately prior to issuance of the new guidelines, we reviewed the medical records of 2925 patients sampled from a population of over 14,000 hypertensives following in a network of nine primary care clinics operated by the Harris County Hospital District in Houston, Texas. Variables extracted from the medical record included: systolic (SBP) and diastolic (DBP) blood pressure at the initial clinic visit, average of all BP readings in the 12 months prior to the chart review (the measure of current control), antihypertensives prescribed at the most recent visit, and patient sociodemographic variables. The mean age of the sample was 61.6 +/- 12.8 years, and 67% were female. Average 12-month SBP and DBP were 141 +/- 14.7 and 83.6 +/- 8.5 respectively. Forty-nine per cent of patients had SBP controlled to < 140 mm Hg, 79.5% had DBP controlled to < 90 mm Hg, and 46% of patients achieved the criterion of < 140/90 mm Hg. In logistic regression analysis, age, baseline BP, body mass index and ethnicity, but not gender, were associated with current control. After adjustment for other covariates, Hispanics and Black people were significantly more likely to be in poor control than whites (ORHISP = 2.05, 95%Cl = 1.57-2.70; ORBlack = 1.48, 95%Cl = 1.21-1.81). Twelve per cent of patients were not receiving any antihypertensive medication. Of the remaining, the majority (52%) were on monotherapy. In the monotherapy group, 45% had SBP > or = 140 mm Hg and 16% had DBP > or = 90 mm Hg. We conclude that the achievement of new treatment recommendations will require education of primary care providers in more aggressive titration of antihypertensive medications to control SBP.