Spectrophotometric, colorimetric and densitometric methods for the determination of hydrochlorothiazide, benzydamine hydrochloride and clonazepam in the presence of their degradation products are described. Hydrochlorothiazide was determined in the presence of its degradation products methoxyhydrothiazide, hydroxyhydrothiazide and 5-chloro-2,4-disulfonamidoaniline applying the first and second derivative spectrophotometer at 278.8 nm and 254.4 nm, respectively, while benzydamine hydrochloride was determined in the presence of its toxic photodegradation products 5-hydroxybenzydamine and 2-B-dimethylaminopropyl-l-benzylindalolin-3-one colorimetrically using the acid dye bromophenol red and measuring the absorbance of the chloroform solution of the ion-pair formed at 425nm. Clonazepam was determined densitometrically in the presence of its degradation products carbostyril and 2-amino-2-chloro-5-nitrobenzophenone. The suggested methods determine hydrochlorothiazide, benzydamine hydrochloride and clonazepam in the presence of degradation products with mean accuracies of 99.57±0.51%, 100.04±0.41%, 100.03±0.21% and 99.84±0.34%, respectively. The proposed methods are suitable for stability testing in bulk powder and in pharmaceutical preparations.