Abstract Phenothiazines previously separated by thin-layer chromatography were detected on the plates by photochemical derivatization and gave different R F values in six solvent systems. The methanol—acetic acid (95:5, v/v) system gave the best separation and greatest chromatic and fluorescence intensities. Qualitative and quantitative information about propiomazine, acetopromazine and chlorpromazine was obtained by image analysis. Images were obtained with a charge-coupled device camera (CCD) under different conditions using both pseudocolour red—green—blue (RGB) and grey-scale tones and then filtering the light emitted when the derivative spots were excited by UV light. Calibration graphs for acetopromazine were linear from 3.94 to 22.00 m M, for chlorpromazine from 2.69 to 13.00 m M and for propiomazine from 3.31 to 15.00 m M.