A multicenter double-blind randomized trial was performed in 22 teaching hospitals to compare the clinical effectiveness of the combination of amoxicillin (CAS 26787-78-0) plus bromhexine (CAS 3572-43-8) versus amoxicillin alone given 4 times a day for 5 to 7 days in the treatment of clinically diagnosed community-acquired bacterial lower respiratory tract infections. 392 adult patients diagnosed clinically to have acute bronchitis or pneumonia of bacterial etiology were recruited for the study with 192 subjects given amoxicillin (250 mg) plus bromhexine (8 mg) (Drug AB) and 200 receiving amoxicillin (250 mg) (Drug AA) alone 4 times a day for 5 to 7 days. Clinical response, improvement in symptom scores using a visual analogue scale, and bacteriologic response were monitored at Days 3, 5 and 7 of treatment. Results showed that although 180/192 (94%) given Drug AB and 185/200 (93%) given Drug AA had favorable clinical response at the end of treatment, the infection was completely resolved for 89/192 (46%) among the Drug AB group and in 67/200 (34%) of patients on Drug AA (p = 0.022). Also, patients given Drug AB had significantly greater reduction of their symptom scores at Day 3 for symptoms of cough discomfort, cough frequency, ease of expectoration and sputum volume. Among the subset of patients with pneumonia, the cure rates for Drug AB and Drug AA were 24/50 (47%) and 11/50 (22%), respectively (p = 0.008). A respiratory pathogen was cultured in only 72/392 (18%) of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)