The British Thoracic Society (BTS) guidelines for the treatment of community-acquired pneumonia recommend initial therapy with a betalactam antibiotic, with the addition of erythromycin if there are features of an atypical pneumonia. To see if these guidelines were being followed, a prospective study was undertaken of all adult patients admitted to hospital over a 3-month period who were given erythromycin for a community-acquired lower respiratory tract infection. Erythromycin was given to 62 patients who could be fully assessed. Continued prescription of erythromycin was justified in 10 (16%)--two patients with penicillin allergy, two with M. catarrhalis infection and one patient with legionnaires disease. Five patients had infections severe enough on admission to warrant combined therapy in line with the BTS recommendations. Five patients had erythromycin stopped on day 2. Erythromycin was prescribed on admission and continued unnecessarily in 47/62 patients, showing that the BTS recommendations are not being followed correctly.