Despite the importance of lower respiratory-tract infection (LRI) in causing hospitalizations in elderly patients (>or=65 years of age) and recent advances in vaccine development, a complete picture of the causative organisms is not available. All hospital discharge diagnoses (ICD-10 code) for LRI in elderly patients in England during 1995-1998 were reviewed. Using known seasonality in potential causative agents of LRI, the contribution of different respiratory pathogens to hospitalizations coded as 'unspecified LRI' was estimated by multiple linear regression analysis. Ninety-seven per cent of 551633 LRI-associated diagnoses had no specific organism recorded. From the statistical model the estimated proportions of admissions attributable to different pathogens were applied to calculate estimated hospitalization rates: 93.9 hospitalizations/10000 population aged >or=65 years due to S. pneumoniae, 22.9 to influenza virus, 22.3 to H. influenzae, 17.0 to whooping cough, and 12.8 to respiratory syncytial virus. There is enormous potential to improve health using existing vaccines and those under development.