This study investigated the effect of low dose of budesonide 100 micrograms b.d from a new multi-dose dry powder inhaler (Airmax) and from a conventional inhaler (Turbuhaler) on bronchial hyper-responsiveness, lung function and asthma symptoms in mild stable asthmatics. Twenty-five patients were enrolled into a double-blind double-dummy crossover study with two 4-week treatment periods separated by a 4-week washout. Patients had a mean forced expiratory volume in 1 s (FEV1) of 91 +/- 13% predicted, had previously received inhaled short-acting beta 2-agonists only and had a PC20 to adenosine 5' monophosphate (AMP) < 40 mg/ml. PC20 AMP was assessed at baseline, and at the start and end of each treatment period. Patients recorded peak expiratory flow and symptoms throughout the study. There was a mean increase in PC20AMP from start to end of 3.49 doubling dilutions (DD) in the Airmax group and 2.90 DD in the Turbuhaler group. The difference was 0.60 DD (95% CI--0.47, 1.69) favouring Airmax and the upper limit exceeded the equivalence limit of +/- 1 DD. There were similar improvements in FEV1, daily PEF and symptoms in both groups. The majority of patients preferred treatment with Airmax to Turbuhaler (64 vs. 23%). Both treatments were equally well tolerated. In conclusion, 100 micrograms budesonide bid during 4 weeks from Airmax effectively attenuates the response to AMP in mild asthmatics. Overall Airmax offers equal clinical benefit to Turbuhaler.