Bronchodilator efficacy of salbutamol (200 pg), salmeterol (50 pg) and ipratropium bromide (40 pg) aerosols has been compared in 16 patients with stable chronic obstructive pulmonary disease (COPD) using a double-blind placebo controlled cross-over design. When absolute changes in FEV~ were used as the response criterion, efficacy of the three drugs was significantly better than placebo (P<0.05). The onset of hronchodilatation after ipratropium bromide was slower than after salbutamol, but ipratropium induced more and longer-lasting bronchodilatation than the adrenergic drug. Saimeterol was slower but its duration was longer than salbutamol. The onset of the effect of salmeterol was slower than ipratropium bromide, but salmeterol showed, on average, superior bronchodilator efficacy compared with the antichofinergic agent, sustaining hronchodilation longer than ipratropium bromide (responses to salmeterol were significantly (P<0.05) greater than those to ipratropium bromide from 4-12 h time period, but from 15 rain to 1 h time periods response to ipratropium bromide exceeded salmeterol). The mean FEV~ area under the curve was significantly (P<0.05) larger after salmeteroi when compared to ipratropium bromide and salbutamol. Moreover, the mean FEVt area under the curve after ipratropium bromide was significantly (P<0.05) higher than that after salbutamol. In any case, our data showed individual differences in patient response. We conclude that salmeterol compares favourably with ipratropium bromide in terms of effects on lung function at clinically recommended doses because it has a longer duration of action than ipratropium bromide. The longer dosing intervals, which may enhance compliance, encourage its administration in patients with COPD.