We examined immunoglobulin G (IgG) and its subclasses IgG1-IgG4 in the group of asthmatic children aged from 6 to 16 (n = 50) before of specific (mite) immunotherapy and in control group (n = 150) The results showed isolated decrease of IgG2 (22%) and connected with deficiency of other subclasses (16%). After immunotherapy during 3 years we showed deficiency of IgG subclasses in 60% children with asthma. In our opinion IgG should be examined before decision about immunotherapy because its deficiency in spite of good results of immunotherapy may be conductive for recurrent respiratory tract infections. In these cases immunocorrection methods should be considered.