Cough is a common respiratory symptom, the mechanism of which is poorly understood. In this study the role of 5-HT3 receptors was investigated. Capsaicin-induced cough and increase in airways resistance were measured in six male volunteers before and after infusion with granisetron 160-mu-g kg-1 or placebo. Neither cough nor the increase in respiratory resistance was altered by the active treatment. These results suggest that 5-HT3 receptors are not involved in these two respiratory responses to inhaled capsaicin in humans.