Abstract: Large deviations have been found in organized comparisons at a national levelof results of measurements of beta-activity of ~(90)Sr-~(90)Y used as low level referencesource. Based on results of research carraied out at this institute, reasons for such adeviation are analysed, and recommendations are made to increase the accuracy ofthe determination of beta-activity, such as the use of a set of standards of diffe-rent levels of activity as reference sources to match the level of beta activityencountered in each determination.