ABSTRACT.The need for a comprehensive description of blood glucose control on the basis of blood glucose measurement has dramatically increased with the improved methods for blood glucose monitoring and the new devices for blood glucose regulation in diabetics. Blood glucose concentrations measured at approximately equidistant sampling times over a number of consecutive 24‐hour periods were analysed by a computerized method for time series analysis. This enabled an exhaustive, though simple description of the blood glucose variation based upon linear correlations between successive measured values and values measured with 24 hours interval. The method describes the day to day variation in blood glucose control as well as the blood glucose oscillations within the day. This information may be used to define in particular patients, patient groups and in normals the “degree of blood glucose control” which is the quantitative measure of the strength of the linear correlations mentioned above. Quantitative measures of the deviations in blood glucose control in patients from that found under comparable conditions in normal subjects then define the “goodness of blood glucose control”. These methods have been used for an evaluation of the blood glucose control in 10 normal subjects and in 8 type 1 diabetics treated with porcine insulin during one period and with human insulin during another period. Regimes with human and porcine insulin resulted in the same degree of control in the diabetics. The correlations which define the degree of blood glucose control were, on an average, of the same magnitude in the diabetics as in the normal controls. The “goodness of blood glucose control” in terms of mean blood glucose level and the unpredictable blood glucose variation was clearly inferior in the patients compared to the normals. However, a precise definition requires further experience with the method on diab