Abstract: The computer-aided convolution curve method has been applied to the determination of phenacetin, aminopyrine, caffeine and phenobarbitone in the tablet of somidon without prior separation.The convolution curve method is a compound difference method developed on the basis of Glenn's orthogonal function using computer imformation treatment technique.The corresponding average recovery and the coefficients of variation were as follows: 99.96, 0.36% for phenacetin; 99.76, 0.43% for aminopyrine; 99.98, 0.48% for caffeine and 99.26, 0.89% for phenobarbitone.