In a randomized, multicenter, open-label study, 490 ambulatory adult patients with lower respiratory tract infection (LRTI) were randomized to roxithromycin (ROX) 150 mg b.i.d. orally (n = 244) or amoxicillin plus clavulanic acid (AMX + CA) as 500 mg AMX + 125 mg CA t.i.d orally (n = 24). Clinical results were analyzed in 477 patients with acute bronchitis (79%), chronic bronchitis (CB) (14%), and pneumonia (7%). There were significantly more patients with underlying disease (cardiovascular diseases, p = 0.045; and alcoholism, (p less than 0.001), and more patients over the age of 65 years (p = 0.045) in the ROX group. Overall clinical efficacy was similar in both groups: 88% (206:235) in the ROX group and 85% (205:242) in the AMX + CA group. Side effects were reported in 67 cases (28%) in the AMX + CA group and in 21 cases (9%) in the ROX group (p less than 0.0001), causing withdrawal in 21 and three cases, respectively (p less than 0.001). Thus, despite being administered to a significantly older and more ill group of patients with LRTI, roxithromycin was as effective as amoxicillin plus clavulanic acid and better tolerated.