Objective: This study was undertaken to compare the efficacy and tolerability of telmisartan, a novel antihypertensive agent, and atenolol, a well-established beta-blocker, in the treatment of mild to moderate hypertension. Methods: This 26-week, multicenter, randomized, double-blind, double-dummy, parallel-group, titration-to-response study compared doses of telmisartan (40 mg titrated to 80 mg titrated to 120 mg) with atenolol (50 mg titrated to 100 mg) required to achieve diastolic blood pressure (DBP) control (less than or equal to 90 mm Hg or a decrease from baseline of greater than or equal to 10 mm Hg). Open-label hydrochlorothiazide (HCTZ) 12.5 or 25 mg was added if needed according to a prespecified titration rule. Men and women aged >18 years with mild to moderate hypertension (morning mean supine DBP [SDBP] greater than or equal to 95 mm Hg and less than or equal to 114 mm Hg) were eligible to participate. Patients with significant cardiovascular, metabolic, hepatic, or renal dysfunction or chronic obstructive pulmonary disease were excluded. The primary efficacy end point was trough SDBP response at 26 weeks; secondary efficacy end points included changes from baseline at trough in both standing and supine DBP and systolic blood pressure (SBP), and heart rate after 4, 8, 16, and 26 weeks; SEP control (reduction from baseline of greater than or equal to 10 mm HE); normalization of supine SDBP to less than or equal to 90 mm I-Ig; and the need for add-on HCTZ. Changes in quality of lift: were also examined. Adverse events were obtained from spontaneous reporting and recorded. Serious adverse events were reported to the sponsor according to predefined timelines. Results: A total of 533 patients from 49 centers participated. Patients' mean age was 57.9 years (range, 22-79 years); 55.9% (298/533) of the population was male and 98.1% (523/533) was white, Of the 533 patients randomly assigned to treatment and included ill the safety analysis, 520 (97.6%) were included in the efficacy analysis; 346 received telmisartan and 174 received atenolol. A total of 489 patients (91.7%) completed the study (325 [93.9%], telmisartan; 164 [94.2%], atenolol). Pull SDBP response (trough SDBP less than or equal to 90 mm Hg and/or a reduction from baseline of greater than or equal to 10 mm Hg) was observed in 84% and 78% of telmisartan- and atenolol-treated patients, respectively; this difference was not statistically significant. Final SBP/DBP reductions of 20.9/14.4 mm Hg were observed for the telmisartan regimen versus 16.7/13.3 mm Hg for the atenolol regimen; only the difference in SEP was significant (P = 0.005). Reduction from baseline in SEP of greater than or equal to 10 mm Hg was achieved by 80% of telmisartan-treated and 68% of atenolol-treated patients (P = 0.003). Adverse events were reported by 52.7% of patients given telmisartan and 61.2% of patients given atenolol; this difference was not statistically significant. Most events were mild or moderate. Although fatigue and male impotence were more common in atenolol-treated patients (3.4% and 4.0%, respectively), the incidence of these adverse events was too low to differentiate statistically. Conclusions: Telmisartan appears to be at least as effective as atenolol in the treatment of mild to moderate hypertension and may be better tolerated.