Twenty patients (six severe asthma, 14 chronic obstructive pulmonary disease, COPD) were referred for consideration of domiciliary nebulized treatment. A double blind laboratory assessment demonstrated similar subjective and objective responses to nebulized salbutamol (5 mg), ipratropium bromide (IB) (0.5 mg) or a mixture of these medications in both groups of patients. The patients subsequently self-administered each treatment four times daily for one month. Fourteen patients requested long-term home nebulizer treatment (three salbutamol, four ipratropium bromide, seven mixture), and nine of these had their highest domiciliary peak flow recordings during home nebulizer treatment. However, subjective and objective laboratory assessments did not clearly predict the patients long-term choice of therapy in any case. There was little overall correlation between the laboratory response and the domiciliary response to treatment (Spearman correlation coefficient; subjective score, laboratory vs. home, r = 0.27, P = 0.03; peak flow response 30 min after treatment, laboratory vs. home, r = 0.31, P less than 0.02). The hospital study was also unreliable in predicting side effects during domiciliary nebulizer use. We conclude that prospective laboratory studies are of little value in the assessment of patients for home nebulizer therapy; these assessments must be made by carefully supervised domiciliary trials of nebulized treatment.