In the first part of the publication the rheological properties of the vehicles used for the production of suppositories were studied in order to determine the ideal parameters for formulation. In this part a detailed methodology and the results of the in vitro membrane diffusion and in vivo bioavailability studies, are presented. The results confirm a general correlation between the in vitro and the in vivo findings. It seems that hydrophilic macrogol-mixture with great molecular mass can be recommended as the optimal vehicle for formulation of diazepam suppositories.