Sixteen adults who had chronic asthma with nocturnal symptoms were selected to evaluate and compare the effectiveness of 7 A.M. versus 7 P.M. single daily dosing with the 24-hour sustained-release theophylline Uniphyl. The study was a randomized, double-blind, placebo-controlled trial in which the patients were given 800 mg of Uniphyl at either 7 A.M. or 7 P.M. for one week each. Serum theophylline levels showed significantly higher peak (18.1 +/- 1.8 micrograms/ml versus 12.7 +/- 1.2 microgram/ml) and trough (12.4 +/- 1.3 microgram/ml versus 7.6 +/- 1.0 microgram/ml) concentrations during evening dosing. Furthermore, daily peak flow values were higher in the morning when Uniphyl was given at 7 P.M. Thus, nocturnal dosing with Uniphyl gives higher serum theophylline concentrations and, with this, better control of nocturnal asthma.