A double-blind comparison of betamethasone valerate, sodium cromoglycate and the combination of these two treatments was carried out in twenty-two adult patients with asthma. Regular fortnightly assessments were made in the clinic throughout the study and adrenal function was monitored and found to be normal. All patients measured their peak expiratory flow rates in the morning and evening and monitored their symptoms daily on a record card as well as recording bronchodilator usage. Assessment using these parameters indicated that treatment with betamethasone valerate compared with sodium cromoglycate resulted in an improvement in the patients’ asthma which was statistically significant (P<0.001). Overall the combined treatment produced a better response than sodium cromoglycate (P<0.02) but a poorer response compared with the steroid aerosol given alone (P>0.05). In only two patients was the response to the combined therapy significantly greater than to either drug given alone.