Techniques for obtaining satisfactory performance from radioactivity-counting systems are described. Acceptable performance is maintained by routine tests of background and standards combined with the application of statistical criteria of acceptability. The use of control charts in conjunction with the test data is recommended to facilitate determination of satisfactory instrument and sample measurements. Corrective adjustments are made when necessary to assure continuity of reproducible results, which is particularly important for long-term studies. Methods of chart application and interpretation of plot patterns are outlined. Requirements for the design of counting laboratories, suitable performance standards, and associated control measures are also discussed. (Author)