Seratrodast, an antagonist to thromboxane A2 (TXA2) receptors, is not always effective in patients with bronchial asthma. In fact, some respond definitely to this drug while others not. In the present study, to clarify the predictability of the clinical effects of Seratrodast, we investigated whether there is a correlation between the levels of TXB2 and 11-DHTXB2, both of which are metabolites of TXA2, in urine and sputum taken before the administration and the clinical effects seen after initiation of the treatment. Baseline concentrations of TXA2 metabolites in urine/sputum were not significantly different between responders and non-responders. However, 4 cases who had remarkably responded to Seratrodast had significantly higher baseline 11-DHTXB2 levels than the rest of the patients. These results suggested that bronchial asthma patients with high urinary 11-DHTXB2 levels could markedly respond to Seratrodast treatment.