A method for the determination of theophylline and promethazine in suppositories is proposed which allows the determination of both components in a single suppositorium. The ingredients were extracted by hot water and addition of a little bit of sulfuric acid. Theophylline is determined potentiometrically without separation of promethazine by titrating the acid which is set free after addition of silver nitrate. Promethazine is separated by ether in alkaline medium, reextracted in HCl (0,1 mol/l) and determined colorimetrically. The precision of both methods is good. The results of the determination in the suppositories are given.