In the present part of our series of papers a study on theophilline containing suppositories prepared in pharmacies is described. From the possible methods for assay of theophilline two nonaqueous titrations are compared. In first, theophilline is measured as a very weak base in a mixture of glacial acetic acid and acetic anhydride with perchloric acid using Sudan-III indicator, in second, the compound is measured as medium strong acid in dimethylformamide solvent with sodium-hydroxide titrant using phenolphtalein indicator. These methods were validated and the first was found more appropriate for regulatory control. We investigated suppositories prepared in our laboratory and in different pharmacies. The study revealed the poor quality of the preparations due to the difficulties in the technology and the importance of the applied vehicle. A guideline for the good preparation practice and an alternative technology are proposed.