Fifty-one children aged 4–12 years, presenting with an acute epidose of chronic rhinosinusitis, were treated for 6 months with either Broncho-Vaxom® (BV; marketed in Yugoslavia under the trade mark of Broncho-Munal®) or placebo under double-blind randomized conditions. The efficacy of BV was assessed on the basis of clinical symptoms (cough, nasal discharge, congestion of nasal mucosa), number and duration of concomitant treatments (antibiotics, secretolytics, antitussives), number and duration of acute episodes during the trial and serum IgA levels. In BV treated patients the incidence and duration of infectious episodes and the number and duration of concomitant treatments decreased significantly in comparison with the placebo group, and the clinical response correlated positively with an increase in the serum levels of IgA. The results of treatment of acute episodes of chronic rhinosinusitis in children demonstrated the curative and prophylactic efficacy of