In the course of the drug form development of newly synthetized potential drugs the influence of the auxiliary substances, glycerol (GL), propylene glycol (PG), and sorbitol (SO) in concentration of 5, 10, 15 and 20%, on the partition coefficient (P') of some phenylcarbamic acid derivatives was studied. Because of the great variations of this influence, attempts were made to find optimal additive for the further processing. The obtained values of P' show that an optimal additive for the drug H+B seems to be SO while in the case of the substances XIX M and XIX the optimal additives are PG or GL and SO, respectively.