Trials of the coagglutination test for the identification of Bordetella bacteria and for the detection of B. pertussis in the material from healthy and sick children have demonstrated the possibility of using this test for the detection of B. pertussis in mixed cultures on the third day after preliminary inoculation in the growth medium (casein-coal agar) and as a test for the differentiation between B. pertussis and gram-negative bacteria similar to it by their morphologic and serologic characteristics.