Bitolterol is a beta-adrenoceptor agonist which is hydrolysed to colterol by tissue esterases present at high concentrations in the lung. Animal studies indicate that bitolterol has significant beta 2-selectivity. In initial clinical trials transient cardiovascular effects have occurred in about 5% of patients. The spectrum of other adverse reactions with bitolterol is similar to that found with other beta-adrenoceptor agonists. Preliminary therapeutic trials of bitolterol administered by aerosol or nebuliser in adult patients with asthma have shown variable but significant improvements in forced expiratory volume in 1 second (FEV1) and a duration of action of up to 8 hours in some patients. Bitolterol has been shown to provide similar maximum increases in FEV1 to isoprenaline (isoproterenol) and to be significantly longer acting in long term comparative trials. Either alone or in combination with oral theophylline, bitolterol aerosol produces greater and more prolonged bronchodilation than oral theophylline alone but more consistently in non-steroid-dependent patients. Duration of bronchodilation with bitolterol in patients receiving steroids is less than in those who are not steroid dependent, perhaps due to more severe disease in the former group. More long term trials in larger groups of patients are clearly needed to assess the efficacy and safety of bitolterol in comparison with other long acting beta-adrenoceptor agents, and to define the role of bitolterol in the combination regimens of antiasthmatic agents which are becoming increasingly popular. Nevertheless, bitolterol appears to be a well tolerated and relatively long acting alternative to other beta-adrenoceptor agonists in the treatment of reversible obstructive airways disease.