The effects of a new inhaled antimuscarinic drug, oxitropium bromide, and of a slow-release theophylline preparation upon nocturnal asthma were compared in a placebo-controlled double-blind study. Two samples were studied: 12 patients received oxitropium at 600 micrograms (6 subjects) or at 400 micrograms t.i.d. (6 subjects) whereas 11 received theophylline at 300 mg b.i.d. Morning dipping, assessed by the fall in peak flow overnight, was significantly reduced in the periods when either active drug was taken, whereas no difference was noticed during the placebo administration. No significant difference was noticed between results obtained with either active drug, as well as with either dosage of oxitropium. No subject reported side effects of oxitropium, as compared to three subjects reporting nausea, vomiting and tremors after theophylline. Oxitropium proves to be a valuable alternative to theophylline in nocturnal asthma, since it is equally potent, safer and does not require the titration of dosage.