1 In a double-blind placebo controlled dose-response experiment in six asthmatic patients with reversible airways obstruction the effect of i.m. salbutamol (4 mug/kg, 8 mug/kg or 12 mug/kg) was assessed by improvement in spirometry and change in pulse rate. 2 Salbutamol (8 mug/kg) resulted in a mean increase in FEV1 of 1 litre and a mean increase in pulse rate of 7 beats/minute. 3 It was concluded that salbutamol (8 mug/kg) was the optimal dose.