Eleven patients with bronchial asthma and 10 with chronic bronchitis were treated over four consecutive 3-day periods, firstly with aerosols either of ipratropium bromide (40 microgram four times a day) or of salbutamol (200 microgram four times daily) by random allocation, then the alternate drug, next by both drugs together, and finally with prednisolone (10 mg three times daily) in addition to both drugs. The effects of these four treatment periods were assessed both clinically and by measuring ventilatory capacity, nitrogen slope and progressive exercise testing. Ipratropium bromide and salbutamol produced approximately equal improvements in both diseases, with salbutamol showing a marginal advantage in patients with asthma. The combination of both drugs together more than doubled the FEV1 change in both groups of patients. The addition of prednisolone to both drugs produced a marginal advantage only in those with asthma.