A new oral bronchodilator, clenbuterol, was compared with terbutaline during a 5-week single-blind crossover study in 16 patients with chronic airways obstruction and with cough and sputum production. After a run-in period (1 week), the study was performed in two separated 2-week periods (Phase II and Phase IV), separated by a 1-week drug-free period. Oral clenbuterol was administered at 20 to 30 micrograms 3-times daily, oral terbutaline at 2.5 to 5 mg 3-times daily. The forced expiratory volume in 1 second (FEV1) was measured at the beginning and end of Phase II and Phase IV under baseline conditions, and 1 hour after an oral dose of clenbuterol or terbutaline. Parents recorded subjective and objective information in a daily diary and used no bronchidilator therapy for 12 hours before each visit. Clenbuterol and terbutaline significantly improved baseline FEV1 and the bronchodilator effects of single oral doses were similar. The mean dyspnoea, cough and sputum score values after treatments were lower than during the wash-out period (p less than 0.05). Tremors were noted in 6 patients on clenbuterol and 5 on terbutaline. It is suggested that clenbuterol is a good alternative oral drug for treatment of chronic airways obstruction.