Community-acquired respiratory infections are usually treated empirically by the primary care physician. Increasing antibiotic resistance, for example, in pneumococci, prompted a UK survey of antibiotic susceptibility of three major lower respiratory tract pathogens, Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Each of 27 centres was asked to collect up to 100 isolates of the three species and submit them for confirmation of identity and for susceptibility testing to a central laboratory. In addition, general practitioners were asked for demographic details on the patient, their treatment and the clinical outcome. Of 1689 viable pathogens collected, there were 1078 (64%) strains of H. influenzae, 258 (15%) of M. catarrhalis and 353 (21%) of S. pneumoniae. Production of beta-lactamase was detected in 163 (15%) of 1078 isolates of H. influenzae and in 243 (94%) isolates of M. catarrhalis. For S. pneumoniae, moderate resistance to penicillin (MIC 0.12-1 mg/l) was found in 12 (3.4%) isolates and high level resistance (MIC > or = 2 mg/l) in 13 (3.7%) isolates. The most common individual treatments were amoxycillin, amoxycillin/clavulanate (amoxyclav) , and erythromycin. Complete or partial clinical resolution was achieved in 88% of 809 patients infected with H. influenzae, 83% of 197 infected with M. catarrhalis and 90% of 255 infected with S. pneumoniae.