Perindopril has been determined in the presence of its acid induced degradation products using a first derivative (D₁) spectrophotometric method ( method I) or colorimetric methods( methods II and III). The spectrophotometric method is based on D₁ value measurement at 220 nm. The colorimetric methods are based on either the reaction of perindopril with iron (III) chloride in the presence of potassium thiocyanate to form orange complex that is soluble in chloroform with maximum absorbance at 432 nm (method II) or the formation of an ion-association complex with bromothynmol blue at pH 5 which is extracted into chloroform and has maximum absorbance at 418 nm ( method III). The three methods have proved to be stability indicating, since plots of log C% versus time were linear. The application to perindopril in tablets gave good results.