The two-decade history of federal clinical laboratory standards is associated with improved laboratory performance. At present, there is limited empirical evidence explaining which regulatory requirements have contributed to this improvement. Some evidence suggests a cause-and-effect relationship for certain standards, eg, participation in proficiency testing, but not for others. Further improvements in performance and evolutionary changes in standards can be anticipated. The federal rule-making process properly emphasizes fairness and participation. As a result, the standard-setting process may not keep pace with rapid technological and utilization changes now in progress. A shared goal of laboratorians and policy makers is to "do no harm!" Empirical evidence is likely to play an ever increasing role in meeting this goal, which will require identifying effective and cost-efficient standards for laboratory performance.