Fifteen patients with asthma were given salbutamol controlled-release (SCR) 4 mg or 8 mg twice daily for seven days, in a randomised double-blind cross-over design. Plasma salbutamol levels were measured after the first and fifteenth doses for a 12 h period following drug ingestion. At steady-state the geometric mean values for Cmax were 8.2 ng/ml for 4 mg, and 16.1 ng/ml for 8 mg. Median tmax values were 300 and 240 min respectively. The geometric mean AUC (0-12) were 4507 ng.min.ml-1 and 8980 ng.min/ml. Peak to trough fluctuation ratios were 0.577 and 0.572. There were no significant differences between 4 mg or 8 mg formulations, for any of the parameters measured, after appropriate corrections for dose. The concentration-time profiles at steady-state showed little fluctuation in plasma salbutamol levels over the twelve hour dosing interval. These results show that 4 mg and 8 mg formulations of SCR provide smooth plasma profiles at steady-state with a twice daily dosing regime.