The administration of Bordetella pertussis vaccine to mice has been associated with the development of an impaired beta-adrenoceptor responsiveness and in many respects has resembled human asthma. Trachea (n = 12) were isolated from Swiss-Webster mice 5 days following the intraperitoneal administration of 2 x 10(9) B. pertussis organisms. The tracheal smooth muscle response to carbachol was measured and compared with that found in trachea from unvaccinated mice (n = 15). The contractile response was similar in both groups. The tracheal smooth muscle relaxant effects of isoproterenol were measured in these two groups. The EC50 value for isoprenaline (6.5 x 10(-7) M) in trachea from B. pertussis treated mice was significantly (P < 0.05) greater than that noted in the control animals (2.3 x 10(-7) M). These studies demonstrated that in tracheal smooth muscle isolated from B. pertussis vaccinated mice, the relaxant effects of isoprenaline are impaired.