In a double-blind cross-over study 20 patients with reversible airways obstruction were treated either with conventional 4 mg tablets of salbutamol a.i.d., or 8 mg controlled release (CR) tablets of salbutamol b.d. Each treatment was given for 2 weeks. The morning PEFR was significantly higher with the CR tablets (p<0.05) but although the evening PEFR was also better the difference was not significant. Wheeze was significantly lower (p<0.05) and extra “rescue” inhalation of bronchodilators was required less often and on fewer occasions during treatment with the CR tablets. Comparison of the 12-h mean plasma salbutamol profile showed a peak and trough every 6 h with the standard tablets, and a flatter profile with a single, lower and delayed peak during the 12 h between CR tablets. Although the minimum and average plasma salbutamol levels were similar in the groups on the two preparations, the maximum plasma level was significantly lower and there was significantly less fluctuation on CR tablets (p<0.02). The CR and standard tablets had equivalent bio-availability.