The results of serological tests for the detection of antibodies against pertussis toxin by means of the ELISA test, and endotoxin of B. pertussis in the passive haemagglutination test were analysed. The levels of IgG, IgM and IgA antibodies were determined for 95% of serum samples of 108 children in control group (without evidence of respiratory infections) for establishing of the correlation of these with the age of these children. In the light of these data the results were evaluated of testing of 136 serum samples taken from 127 children with suspected whooping-cough. The highest diagnostic importance had the demonstration of high IgA or/and IgG immunoglobulins level against pertussis toxin in ELISA test, or tracing of the rate of rise of antipertussis antibodies in the passive haemagglutination test with B. pertussis endotoxin in children with clinical symptoms of whooping-cough.