Fifteen out of 18 'pink and puffing' patients completed a double-blind, placebo-controlled cross-over trial of diazepam and promethazine for breathlessness and reduced exercise tolerance. Dosages were 25 mg and 125 mg daily, respectively, and each course lasted 2 weeks. Patients with psychiatric or other major medical histories were excluded. Of the 3 patients who did not complete the trial, one died during an exacerbation of breathlessness while taking diazepam, one was withdrawn because of mild hypercapnia while taking placebo, and one suffered intolerable drowsiness while taking diazepam. Of the remaining 15 patients, 6 needed a reduction in dosage because of drowsiness: one of these was taking promethazine and 5 diazepam. Diazepam had no effect on breathlessness and noticeably reduced exercise tolerance. Promethazine reduced breathlessness and improved exercise tolerance without altering lung function. From these results diazepam is contraindicated for breathlessness and reduced exercise tolerance in fixed airways obstruction, but promethazine may be beneficial.