The bioavailability of theophylline following single oral doses of a theophylline capsule, a theophylline tablet, and an aminophylline tablet in beagle dogs was compared against an intravenous standard. Plasma theophylline levels after oral and intravenous drug administration were described by the one-compartment open model. The onset of theophylline absorption from the oral products was rapid. While the theophylline tablet showed a slower absorption rate than the capsule or the aminophylline tablet, all three products appeared to be completely bioavailable.