A group of 18 paired sera, obtained from RSV-infected children were assayed by Western-Blot for antibodies for RSV proteins in the immunoglobulin classes IgG, IgM, IgA and IgE and in the IgG subclasses. The IgG antibodies for the protein G were found in almost half of the sera tested, while in the other immunoglobulin classes the antibodies occurred in a much lower number of the sera. The antibodies for protein F1 were detected first of all in the IgG class and subclasses. The antibodies for protein N were present in the IgG class of about half of sera and antibodies for protein P were found first of all in the IgG and IgM classes. A relatively high number of the sera contained IgE antibodies for protein M. In the first 3 months of life, the children poorly responded to the infection by the production of antibodies for RSV proteins. The most clear response by various immunoglobulin classes to RSV proteins was observed in children 4-12 months of age.