High doses of inhaled beclomethasone dipropionate (BDP) are effective in some patients with chronic obstructive pulmonary disease (COPD). However, dose-response data for this agent are limited. To determine whether patients receive maximum benefit from 1600 micrograms of BDP, we performed a randomized, double-blind, placebo-controlled, cross-over trial. Twenty-one patients with stable COPD [mean +/- SD: age, 69.1 +/- 6.8 yrs; FEV1, 0.86 +/- 0.28 L] were treated with both inhaled bronchodilators and 1600 micrograms of BDP daily for at least 3 months. Each patient received 30 mg of oral prednisolone or a placebo for 3 weeks. In addition to end-point spirometric assessments daily peak expiratory flow rate, symptom scores, and scores on a chronic respiratory disease questionnaire were recorded for the last week of each 3-week period. Oral prednisolone did not improve FEV1, FVC, symptoms or scores on the questionnaire. We conclude that 1600 micrograms of BDP in addition to inhaled bronchodilators produces maximal improvements in stable patients with COPD.