[External quality assurance: a significant--and 25-year-old--element of quality management in the medical diagnostic laboratory].

An external quality assurance system in the medical diagnostic laboratory, which is an essential part of the modern total quality management (TQM) concept in the public health system, was established in Austria already 25 years ago. The development and the scope of this quality assessment system by the "Austrian Society for Quality Assurance and Standardization of Analyses in the Clinical Laboratory" (OQUASTA) are presented. The decreasing coefficients of variation of several parameters of the external quality assessment exercises demonstrate an increasing analytical precision and might be interpreted as an effect of this quality assurance system.