Though infection has declined as a cause of death it consumes a major proportion of primary care resources, and because of antibiotic resistance is increasingly important. We examined the burden of illness attributable to infection in primary care by analysing data from the fourth practice-based national morbidity survey which monitored all consultations by diagnosis in 470,000 persons over a 12 month period from September 1991 to August 1992. Rates of persons consulting, new episodes of illness and consultations were calculated according to the list of infections published by Wilson and Bhopal (W&B list), and as amended by the Communicable Disease Surveillance Centre (CDSC list); selected comparisons were made with national data on hospital derived finished consultant episodes and deaths. Forty-one percent of all registered persons consulted on at least one occasion during the year for infection (estimated by either list). Infections accounted for 40% of all new episodes of illness and 29% of all consultations; respiratory infections accounted for approximately half the infection total. New episode rates were highest in children aged less than 1 year and lowest in males 25-54 years and females 55-64 years. Except in infancy, rates were higher in females. There were 734 episodes of infection annually per 1,000 population reported in general practice compared with 20 per 1,000 finished consultant episodes. The average episode of infection prompted 1.2 general practice consultations. Improved management through more precise diagnosis by near patient tests is desirable, but is unlikely to be obtained cost effectively if consultation numbers or the time spent is substantially increased. These results emphasise the importance of adequate training for general practitioners in the natural history, epidemiology, diagnosis and treatment (pharmacology) of infection.