Clinical and Laboratory Standards Institute document GP35-A--Development and Use of Quality Indicators for Process Improvement and Monitoring of Laboratory Quality; Approved Guideline provides guidance on development of quality indicators and their use in the medical laboratory. These indicators include measures developed in a single laboratory for local use and indicators developed by other organizations and national bodies. The document includes criteria for development of quantitative, ordinal, and qualitative indicators; it also includes procedures for gathering data, presenting and interpreting results, monitoring performance over time, and comparing performance with other laboratories or national norms.