Two acellular pertussis vaccines (SmithKline Beecham 3-component and Connaught 5-component), and a whole-cell pertussis vaccine (Evans), were similarly protective against paroxysmal coughing and leukocytosis in a coughing-rat model of pertussis. A two-dose immunization schedule was followed by sublethal intrabronchial challenge with Bordetella pertussis strain 18-323, encased in fine agarose beads, and the coughing monitored by sound-activated tape recorders. Pertussis toxoid by itself gave some protection against coughing, but lower than that afforded by the vaccines, despite inducing a higher serum anti-PT titre. The other component antigens, given individually, failed to protect against coughing although inducing antibodies. Immunization with the whole-cell and acellular vaccines and with their component antigens, as well as challenge with B. pertussis, caused significant elevation of total serum IgE antibodies. Antigen-specific IgG and IgA were detected in tracheobronchial washings from rats recovering from B. pertussis challenge, but vaccination prior to challenge had little influence on these antibody levels. The coughing-rat model of pertussis may be useful for the comparative testing of different formulations of pertussis vaccines before trials in human infants.