Asthma is associated with an increase in airway blood flow (Qaw), presumably as a manifestation of airway inflammation. We therefore determined the effect of the antiinflammatory agents montelukast (ML) and fluticasone propionate (FP) on Qaw in 12 patients with mild intermittent asthma. Using a double-blind approach, Qaw along with FEV(1) and Vmax(50) were determined before and after a 2-week treatment period with either ML (10 mg/day), FP (440 microg/day), or 10 mg of ML plus 440 microg of FP daily, separated by 2-week washout periods. Mean (+/- SEM) Qaw ranged from 68 +/- 4.2 to 71.8 +/- 5.9 microl x minute(-1) x ml(-1) anatomic dead space before the treatment periods. ML, FP, and ML plus FP decreased mean Qaw by 21.5, 20.8, and 26.9%, respectively (p < 0.05 for all). No significant difference was observed among the three regimens. FEV(1) and Vmax(50) were not changed by any of the treatments. We conclude that at the dosages used, ML and FP are equipotent in reducing Qaw in patients with mild asthma, and that the magnitude of the response is not greater if the two drugs are combined. The results also suggest that the vascular effects of these agents can be assessed independent of their effects on airway function.