Objective To explore the pathogenic effects of granulocyte-macrophage colony-stimulating factor(GM-CSF) in children with pneumonia.Methods The plasma levels of GM-CSF in children (30 cases of slight pneumonia, 20 cases of severe pneumonia complicated by heart failure, and 25 healthy children) were studied by radioimmunoassay.Results The plasma levels of GM-CSF in children with slight and severe pneumonia complicated by heart failure were 12 79±2 02 pg/ml and 9 14±2 39 pg/ml(P<0 01).The levels in the two groups were significantly higher than that in healthy children(7 59±3 13 pg/ml, P<0 01, P<0 05).Conclusions GM-CSF participates in the pathogenesis of penumonia in children.