Granulocytes play a key role in the defence against bacterial infections. Their dysfunction may both predispose to and result from infections. The oxidative metabolism of peripheral blood granulocytes was studied in 50 children aged from 1 to 10 years, with recurrent upper respiratory tract infections and/or tonsillar hypertrophy. Four groups of patients were recruited: 15 healthy controls, seven patients with idiopathic tonsillar hypertrophy, 12 patients with upper respiratory tract infections and 16 patients with upper respiratory tract infections with concurrent tonsillar hypertrophy. The ability of granulocytes to produce reactive oxygen species was assessed by nFMLP-induced chemiluminescence. Both increased and depressed granulocyte activity was observed in all studied groups, with the exception of controls. Altered granulocyte function was observed in 30% of patients in the idiopathic tonsillar hypertrophy group. In children with recurrent infections abnormal chemiluminescence results were found in from 75% to nearly 90% of patients. This preliminary study demonstrates the possible relationship between recurrent upper respiratory tract infections, tonsillar hypertrophy and impaired peripheral blood granulocyte chemiluminescence.