Abstract: A computer-aided convolution curve method has been applied to the determination of 8-chlorotheophylline and diphenhydramine in dimenhydrinate raw material and the double salt in tablet without prior separation. The average recovery and the coefficients of variation for 8-chlorotheophylline were 100.8, and 0.04% and for diphenhydramine were 102.4 and 1.34%, respectively. The present method provides accurate and reliable results comparable to those obtained from the assay defined in the Chinese Pharmacopeia (1985) for five batches of dimenhydrinate.