In steroid resistant chronic obstructive pulmonary disease (COPD) we assessed the effect of q.i.d. domiciliary nebulized fenoterol (F) 1.25 mg and ipratropium (I) 0.5 mg for three weeks in a placebo-controlled, randomized, double-blind, crossover study. The twenty patients studied (mean forced expiratory volume in one second (FEV1) 0.8 l) all showed less than 20% increase in FEV1 to 200 micrograms inhaled salbutamol (S) and less than 20% increase in peak expiratory flow rate (PEFR) after 2 weeks prednisolone therapy. Respiratory function tests, 5 min walking distance (5 MWD), visual analogue scales (VAS) for breathlessness, oxygen cost diagrams and reversibilities were performed weekly for three weeks with patients on their usual therapy, after three weeks domiciliary F+I, after three weeks saline and, finally, after a further three weeks on usual therapy again. Primary end-points, selected prior to unblinding, were mean home twice daily PEFR, trapped gas volume, FEV1 and 5 MWD. Home PEFR rose from 164 l.min-1 on saline to 196 l.min-1 on F+I (p = 0.0001). Secondary end-point analysis revealed a fall in home inhaler usage and a rise in VAS. Using the criterion of +15% and greater than 20 l.min-1 increase in home PEFR, 11 out of 20 patients had a "positive" trial. We suggest that such patients, but not others, benefit from long-term, nebulized beta 2-agonist and ipratropium. Trials using home PEFR recordings should be used to identify them.