UV-spectrophotometry in combination with Kalmanfiltering is used for the assay of analgesics in tablets. Commercial products containing various combinations of acetylsalicylic acid, salicylic acid, caffeine, phenacetine and acetaminophen are analyzed. For comparison, these tablets were also analyzed by HPLC. The accuracy and precision of both methods are comparable. The described spectrophotometric assay with the aid of Kalmanfiltering represents a new, rapid and low-cost alternative to existing analytical procedures for analgesics.