In severe chronic asthma, long-term oral steroids may be necessary to control symptoms. In patients in whom such treatment was under consideration, the efficacy and safety of salmeterol xinafoate 100 micrograms b.i.d. was investigated in a randomized, double-blind, placebo-controlled parallel-group, multicentre study. One hundred and nineteen chronic symptomatic asthmatics were randomized to receive either salmeterol, 100 micrograms b.i.d. (n = 55; baseline % predicted morning peak expiratory flow (PEF) 59%; forced expiratory volume in one second (FEV1) 66%) or placebo (n = 64; baseline % predicted morning PEF 63%; FEV1 66%) both via the Diskhaler. Morning and evening PEF and asthma symptoms were recorded in daily record booklets by the patient over a 12 week period. A significant improvement in morning PEF was achieved after 1 month in the salmeterol treated group; this persisted throughout the treatment period (estimated treatment difference 22 L.min-1). There was a significant increase in the proportion of symptom-free nights experienced by the salmeterol treated group (33 (SD 32) %) compared with placebo (13 (26) %), and a significant decrease in daily use of relief medication (mean decrease 5.1 (4.7) doses per day with salmeterol, 2.5 (4.0) doses with placebo). Both treatments were well-tolerated, with no evidence of any difference in the side-effects associated with beta 2-agonists. In conclusion, the addition of salmeterol (100 micrograms daily) to the existing treatment of chronic asthmatics under consideration for maintenance oral corticosteroid therapy is well-tolerated, improves lung function and provides additional symptom control.