A new way of investigating the enzymatic inversion of sucrose is described. The reaction is followed by measuring the optical rotation of the solution, but instead of taking out samples in which the reaction can be stopped and measuring the optical rotation after the mutarotation of glucose and fructose has stopped, the measurements are performed directly on the reacting solution and a correction for the mutarotation is applied. The expression for the correction term is derived as a second order differential equation which is solved numerically by a step by step integration. The mutarotation constants for glucose and fructose have been determined and using these values and an assumed value for the optical rotation of [beta]-fructofuranose it is shown that the correction term is in accord with experiments.