Montelukast, a specific cysteinyl leukotriene receptor antagonist, has been shown to improve pulmonary function within 1 h of ingestion. This study was undertaken to compare the effects on peak expiratory flow rate (PEFR) of oral montelukast added to intravenous steroid, intravenous steroid alone and placebo during the 24 h period following administration. Seventy asthmatic patients (FEV1 40-80% predicted and > or = 15% improvement after inhaled beta agonist) were enrolled in a single blind study to receive oral montelukast (10 mg) plus intravenous prednisolone (1 mg/kg), intravenous prednisolone (1 mg/kg) or placebo in a randomised fashion. The patients received one ofthe above three groups of medication before any other treatments. This was immediately followed by the aerosol treatments of 100 mcg of terbutaline sulphate divided into three doses during 1 h as described in the consensus statement. Thereafter, patients were observed for 24 h to document the effects on PEFR, Borg dyspnoea score and need for rescue medication. The primary end point was percentage change at different time points. Secondary end points were Borg dyspnoea score and use of rescue medication. Compared with placebo, montelukast added to the prednisolone group and the prednisolone alone group had significant percentage change from baseline in PEFR in the entire 24 h period (P<0.05). The difference in PEFR between montelukast plus prednisolone group and prednisolone group favoured the montelukast plus prednisolone group but did not reach statistical significance. Furthermore, montelukast plus prednisolone group required less inhaled short-acting beta agonistthan other two groups. The results of this study indicate that adding montelukast to steroid in acute asthma may have some additive improvement in lung functions.