Frequent respiratory tract infections in the paediatric population are associated mainly with immune system immaturity. A child aged up to 5 years can have up to 8 respiratory infections in a year. Immunomodulation through the elimination of negative environmental factors is of limited efficacy in the paediatric population. For this reason, in certain cases there is a need for pharmacological stimulation of immune response mechanisms in order to limit the number of infections. Modulators include medication, vitamins and trace elements, probiotics and plant formulations. Unfortunately, there are insufficient scientific data which confirm the efficacy of many such agents. Bacterial lysates are an exception: their effects have been confirmed in well-designed studies. Such formulations consist of killed bacterial cells or fragments of their organelles. Bacterial lysates contain antigens of the most common human respiratory pathogens. The efficacy of a bacterial lysate is the resultant of two components: patient-specific (individual immune reactivity) and formulation-specific (composition, dosing regime). To date, no reliable studies comparing the efficacy of different formulations have been conducted. One of the most thoroughly studied products is the one containing OM-85 lyophilisate (BV, Broncho-Vaxom®).