Within the framework of the study of the derivatives of phenylcarbamic acid with a local anaesthetic effect, one of them, a potential medicinal agent with the working name of XX B, chemically N-[2-(3-heptyloxyphenylcarbamoyloxy)-ethyl]-dimethylammoniumchl oride, was investigated. Linking up with the previous studies, the paper investigated the effects of two auxiliary substances--cellulose derivatives (hydroxyethylcellulose, methylcellulose)--and their concentration on the pharmaceutical availability of the potential drug XX B from the dosage form. At the same time the effect of the employed concentration of the macromolecular substances on the viscosity of the dosage form was examined. The study revealed that with the growing concentration of cellulose derivatives the viscosity of the prepared dosage forms was increased, and the release of the active ingredient was decelerated. Both auxiliary substances influenced the pharmaceutical availability of the potential drug XX B in an approximately identical manner, and thus both could be employed for the same purpose.