The reliability of clinical signs that might be used by village health workers in distinguishing acute lower respiratory infection (LRI) from upper respiratory infections (URI) in children was evaluated. 142 infants and 108 preschool children with LRI and 151 infants and 281 preschool children with URI, attending hospital, were studied. Respiratory rates of over 50/min in infants and over 40/min in children 12-35 months of age, as well as a history of rapid breathing and the presence of chest retractions in both age groups, were found to be sensitive and specific indicators of LRI. Increased respiratory rates and history of rapid breathing were also sensitive in diagnosis of less severe LRI that did not necessitate admission to the wards, whereas chest retraction was not. All these clinical signs had a low sensitivity in diagnosing LRI in children aged 36 months and over.