Abstract: Kalman filtering as a powerful chemometrics tool for state estimation can be used to improve data interpretation ability of the spectrophotometric method of multicomponent analysis. In this paper, a UV-spectrophotometric procedure based on Kalman filtering is proposed for determination of chlorpromazine and promethazine hydrochlorides in synthetic mixtures and pharmaceutical preparations without preliminary separation. The average recoveries calculated at 95% confidence level for chlorpromazine and promethazine were 99.91±0.96% and 99.58±0.97%, respectively. The innovation sequence obtained by the filtering algorithm can provide valuable information about the unknown absorbing species possibly present in the analyzed sample. This information is a very useful criterion for judging the reliability of the results, eg, in the analysis of the deteriorated drug preparations. The proposed method provides an accurate and simple tool for drug quality control.