Abstract First-derivative spectrophotometry is used to evaluate a mixture containing levodopa and benserazide hydrochloride. Levodopa is determined by zero-crossing measurement at 267 nm. The height of the valley at 232 nm is used to calculate the amount of benserazide hydrochloride in mixture. Second-derivative mode is also used to estimate the amount of levodopa. Both drugs are successfully determined in Madopar capsules using first-derivative mode.