1. The purpose of this study was to investigate the involvement of thromboxane A(2) (TXA(2)) in the cough response in a guinea-pig cough model. Here, we describe results obtained using a selective TXA(2) synthetase inhibitor, ozagrel, and a selective TXA(2) agonist, U-46619. 2. Guinea-pigs were anaesthetized and exposed to an aerosol of capsaicin (100 microM) to elicit coughing. The number of coughs was 20.0+/-5.8 during capsaicin provocation (5 min), but only 2. 8+/-0.4 during a 5-min inhalation of phosphate-buffered saline (PBS) (P:<0.05). 3. TXB(2) levels in BAL were 101.4+/-8.0 and 58.4+/-8.7 pg ml(-1) following capsaicin and PBS inhalation, respectively (P:<0. 01), but there was no intergroup difference in the cell populations in BAL. 4. Inhalation of U-46619 did not induce a cough response by itself at concentrations of 100 ng ml(-1) to 10 microg ml(-1). However, it caused a 2 fold increase in the number of capsaicin-induced coughs. 5. To explore the source of the TXA(2), BAL cells were stimulated with capsaicin and the supernatants collected for analysis. The TXB(2) concentration in BAL was increased dose-dependently, indicating that TXA(2) is released from BAL cells in response to capsaicin. 6. Ozagrel was administered orally 1 h before a 5 min capsaicin provocation and the number of coughs was counted during the capsaicin inhalation. Ozagrel decreased the number of coughs dose-dependently (ED(50) value, 26.3 mg kg(-1)). 7. These results show that TXA(2) modulates the capsaicin-induced cough response by increasing capsaicin-sensitivity.