Endotracheal aspirates were obtained from 51 young children for the microbiological diagnosis of pneumonia acquired in hospital or associated with measles or severe protein-energy malnutrition. The procedure proved safe and the information obtained assisted in the management of most cases. There was a fairly good correlation between the findings of Gram stain and those of culture of the aspirates, which improved when only Gram stains showing many or moderate numbers of bacteria were used. The bacteria most frequently isolated were Gram-negative enteric bacilli, Staphylococcus aureus, Streptococcus viridans, Streptococcus pneumoniae and Haemophilus influenzae, many strains of which were resistant to conventional antibiotics. The role of endotracheal aspiration in the microbiological diagnosis of pneumonia in the above-mentioned types of patients is compared with that of percutaneous lung puncture, percutaneous transtracheal aspiration and expectorated sputum.