The objective of this study was to assess the efficacy and tolerability of transdermal clonidine in inner-city African-American and Hispanic-American patients with essential hypertension. A multiclinic open-label, prospective trial for 12 weeks was used. Dose titration was based on office blood pressure (BP) measurements of > 140/90 mm Hg. Clinical sites were community-based primary care centers. Untreated and treated hypertensive patients whose diastolic BP exceeded 90 mm Hg were administered transdermal clonidine at 0.1 mg or 0.2 mg delivery daily. The drug was titrated after 1 month if diastolic BP was greater than 90 mm Hg. At 12 weeks of treatment, change in blood pressure from baseline as well as adverse effects and patient satisfaction were assessed. A total of 357 patients entered the treatment phase of the study, and 315 patients (244 African-Americans, 67 Hispanic-Americans) had evaluable data. Transdermal clonidine significantly (P< .001) lowered BP in all patients by 15.7/12.8 ± 18.1/9.6 mm Hg, and heart rate was reduced by 3 ± 9 beats/min (P< .001). There were no differences in BP reduction according to race and ethnicity, gender, or age. The most common adverse effects were pruritus or discomfort at the patch site, dizziness, dry mouth, and fatigue. Eleven percent of the patients discontinued treatment because of one of these adverse effects. A large proportion of patients (67%) reported that transdermal clonidine was more convenient to use than oral therapy. Transdermal clonidine, alone or in combination with other antihypertensive therapies, significantly lowered BP and heart rate in inner-city hypertensive patients. The drug was generally well tolerated, with 89% of the patients remaining in the trial. Patient acceptability was high with the once-weekly treatment, which is an important feature for this particular hypertensive population.