The mathematical process of differentiation is useful for enhancing the resolution of chromatographic peaks and reducing interferences caused by a slowly changing detector response. Conventional differentiators use fixed time constants and this necessarily means that, when the chromatographic conditions are held constant, later eluting peaks are increasingly attenuated. By using a microcomputer to store chromatograms and calculate derivatives, the time constant of the derivative can be increased through the chromatogram so that the time constant is optimum for the whole of the derivative. Examples from gas and liquid chromatography are given to demonstrate the value of the technique for qualitative and quantitative analysis.