Proficiency testing programs provide many benefits to participant laboratories, functioning as an integral component of total quality control, as a vehicle for self-improvement, as a mechanism for continuing education, and as a fulfillment of regulatory requirements. Proficiency testing should not be utilized as the sole indicator of acceptable laboratory performance; unacceptable results should serve as a trigger for further inquiry and corrective action as indicated. A proficiency testing program should be a broad-based program covering the usual spectrum of laboratory disciplines without commercial bias and it should possess continuous scientific input so as to be capable of adjusting promptly to technologic advancements as well as maintaining established participant benefits. It is important that proficiency testing programs continue to develop mechanisms of mutual interchange with accreditational bodies and regulatory agencies.