Oral capsules containing 100 mg pseudoephedrine hydrochloride and different grades of sodium alginate were prepared and studied to determine drug dissolution, the penetration of dissolution medium into the capsules, and the bioavailability of the formulations in 16 healthy subjects (ages 19-24 yr) using a randomized crossover design. At pH 1.2, there was no difference in dissolution between the formulations. At pH 7.2, release rates correlated with the viscosity grade of sodium alginate. Bioavailability tests confirmed that capsules containing high viscosity grades of alginate led to slow release, with a time to reach peak concn of 6.5 hr, and no loss of amount of drug absorbed. It was concluded that controlled release pseudoephedrine capsules can be prepared with high viscosity grades of sodium