We have studied 164 children with pneumopathy, ranging from one month to 8 years old. They were classified in two groups according as clinical, biological and radiological criteria. Group I (probable bacterial etiology), 65 children; group II (presumable nonbacterial cause), 35 patients. An indeterminate pattern, 64 infants. The CRP was quantified by radial immunodiffusion method. In the group II, lowest CRP values (less than 30 micrograms/ml) were detected in 86% of the patients. In the group I, 88% of the cases offered values over 30 micrograms/ml. The CRP was a sensitive indicator of diagnosis of pneumopathies in children. High CRP values (greater than 30 micrograms/ml) are suggestive of a bacterial etiology, with statistical significance (p less than 0,001).