An open, crossover and randomized study was carried out to compare the safety and efficacy of salbutamol inhaled using the dry-powder inhaler Turbuhaler, and using a pressurized metered-dose inhaler (pMDI). Twelve patients with moderate to severe asthma, aged 47-68 years, were included in the study. On two separate days, patients received a total dose of 1600 micrograms of salbutamol administered in a cumulative dose fashion: 100, 100, 200, 400 and 800 micrograms at 3-min intervals. Salbutamol inhaled via Turbuhaler caused a larger decrease in serum potassium concentration than did salbutamol inhaled via pMDI. The estimated relative dose potency of the hypokalaemic effect of salbutamol Turbuhaler vs salbutamol pMDI was 2.0 with a 95% confidence interval of 1.3-3.6. Turbuhaler caused a small (but statistically significantly greater than with pMDI) increase in heart rate, QTc interval and tremor. Blood pressure was unaffected by the treatments. No adverse events of clinical relevance were reported. The estimated relative dose potency of the bronchodilating effect (FEV1) of salbutamol Turbuhaler vs salbutamol pMDI was 3.0 with a 95% confidence interval of 1.8-5.8. In conclusion, salbutamol inhaled via Turbuhaler was more potent and seemed to have a better therapeutic ratio than salbutamol inhaled via pMDI. Both treatments were equally well tolerated.