A study was done to compare the efficacy and safety of the coprescription of salmeterol 50 microgram twice daily or 100 microgram twice daily with beclomethasone dipropionate (BDP) 500 micrograms twice daily (SALM 50 and SALM 100) with BDP 1,000 microgram twice daily (BDP 1,000) in patients with asthma not controlled by BDP 500 microgram twice daily (or the equivalent). Following a run-in period, 738 patients at 72 centers were randomized to treatment for 24 wk in a double-blind, parallel-group study during which they maintained a daily record of peak expiratory flow rates (PEFRs) and symptom scores. At about 40 of the centers, bronchial hyperresponsiveness (BHR) to histamine was measured during and at 3 and 14 d after stopping treatment. Both groups taking salmeterol showed an improvement of more than 45 L/min in their morning PEFR and 30 L/min in their evening PEFR, compared with respective improvements of 16 L/min and 6 L/min in the group taking BDP 1,000. Both the SALM 50 and SALM 100 groups had a significantly increased percentage of symptom-free and rescue-free days and nights compared with the BDP 1,000 group, and there was no difference between the two salmeterol groups. None of the treatments altered BHR. Exacerbation rates did not differ among the three groups. We conclude that in this selected group of symptomatic patients taking BDP 500 micrograms twice daily, the addition of salmeterol provides better improvement in lung function and symptom control, without altering BHR or increasing exacerbation rates, than does doubling the dose of BDP.