The closed form solution to a mathematical model of a cylindrical membrane device successfully predicts the release profile of benzoic acid. Physically the device consists of a given concentration of benzoic acid in octanol or decanol, bounded by a nylon porous hollow fiber with water-filled pores. The prediction shows excellent agreement with the experimentally derived release profile from two different systems. In comparison to the experimentally derived release profile, the benzoic acid/octanol system prediction gives a maximum relative difference of <5%, and a 3% maximum relative difference in the benzoic acid/decanol case. Predicted results are obtained from the use of the steady state plus the first term of the transient solution (infinite series) and with the use of the first nonzero eigenvalue.