Acute bacterial infection of the lower respiratory tract is a major cause of morbidity and mortality in children and is responsible for 4 million childhood deaths each year. Most of these deaths are caused by pneumonia and occur in the youngest children in the poorest parts of the world. Severe pneumonia is also much more common in low-income countries and is associated with malnutrition, coincident diseases (e.g. human immunodeficiency virus infection), crowding, low levels of health care and high nasopharyngeal carriage of bacterial pathogens.Streptococcus pneumoniaeandHaemophilus influenzaeare the leading bacterial causes of pneumonia worldwide butStaphylococcus aureusand Gram-negative bacilli are not infrequently encountered as aetiological organisms in low-income countries. The major challenge is early diagnosis for timely management with appropriate antibiotic treatment, and although controlled trials have shown that standardised antibiotic treatment reduces pneumonia mortality considerably, its efficacy is limited by the emergence of penicillin and cotrimoxazole resistance. Widespread active immunization with protein-conjugate vaccines againstStreptococcus pneumoniaeandHaemophilus influenzaeis therefore the best hope for limiting the spread of these organisms and reducing the morbidity and mortality of childhood pneumonia in low-income countries. © 2000 Lippincott Williams & Wilkins