Results: The suitable chromatographic conditions for separation of diacefyllin diphenhydramine and theophylline were obtained using a stainless steel column (250 x 4.6 mm), packed with octadecylsilane bonded to porous silica (5 µm); mobile phase: a mixture of 10 volumes of acetonitrile and 90 volumes of formic acide 1% in isocratic mode as mobile phase; flow rate of 1 ml per minute, injection volume of 10 µl; column temperature at 40 oC and detection wavelenght at 274 nm.