A new approach to the measurement of the spatial resolution of a computed tomography (CT) scanner system is presented. The method is based on a direct least-squares fit of an analytical expression to a set of data obtained from a CT image of the interface between two materials. The implementation of the method in connection with the G.E.RTPLAN computer configuration is described. The method has been applied in determining the resolution of an EMI-7070 scanner and it is shown that the assumption of uniformity of the system resolution across the CT image is fulfilled within the accuracy of the present method. The reproducibility of the method has been estimated from a series of spatial resolution determinations performed on ten images taken with identical scan parameters. The standard deviation of this series was 3.2%.