Guinea pigs were inoculated intra-tracheally with bovine parainfluenza type 3 virus (PI-3) to investigate airway responsiveness to histamine and arecoline in vitro. Two days after saline or PI-3 inoculation no difference in the reactivity of the tracheal spirals was observed after cumulative concentration/response curves with both drugs. Similarly, contractions of parenchymal strips, induced by histamine, did not differ between both groups. However, 4 days after PI-3 inoculation the histamine induced contraction of the tracheal spirals was increased by 47% and the arecoline induced contractions by 32% as compared to the control group. Further, the contractions induced by histamine in parenchymal strips were significantly enhanced (p less than 0.01) in the PI-3 treated group. In conclusion, PI-3 infection of guinea pig respiratory tract induces hyperreactivity of the central and peripheral airways in vitro.