The U.S.P./N.F. dissolution test (method I or rotating basket method) and the rotating flask technique (RESO-TEST dissolution method) were applied to four commercial prolonged release theophylline dosage forms. The dissolution data obtained were converted into dissolution efficiencies and submitted to a correlation analysis, the result of which demonstrates the equivalency of both methods with respect to the characterization of the dissolution behaviour of the dosage forms tested. It is suggested to consider replacement of the official dissolution technique, the shortcomings of which are well-known from the literature, by the rotating flask technique.