The simultaneous determination of acetylsalicylic acid (ASA) and its degradation product, salicylic acid (SA) in effervescent tablets by high performance liquid chromatography (HPLC) and UV-multicomponent spectrophotometric (MCS) methods is described. In HPLC method, the analytes were extracted with a mixture of acetic acid and methanol (1:99v/v) and aliquots of these solutions appropriately diluted were injected on a reversed-phase C-18 column using a mobile phase consisting of methanol, water and acetic acid, isocratic elution and detection at 283nm. Recoveries ranging from 98.43 to 101.48 por cento and from 99.13 to 102.80 por cento were obtained from commercial samples for ASA and SA, respectively. Relative standard deviations ranged from 0.94 to 1.31 por cento for ASA and from 1.83 to 2.50 por cento for SA. In MCS method, a mixture of acetic acid and chloroform (1:99v/v) was used as solvent. Analyte solutions were measured at 280 and 310nm. Recoveries ranging from 98.30 to 102.02 por cento and from 98.50 to 103.20 were obtained from commercial samples for ASA and SA, respectively. Relative standard deviations ranged from 0.40 to 0.73 por cento for ASA and from 0.86 to 0.93 por cento for SA. Results were compared statistically by F and t tests. On the basis of precision, accuracy, time saving and economy, MCS method was found to show advantages over the HPLC method and can be applied for routine analysis of commercial samples in quality control laboratories.