Every pulmonary function laboratory should develop and implement a quality assurance program to minimize various technical sources of variation. This article has discussed six major components. First, the education and training of the technologists in the pulmonary function laboratory is probably the most important factor in obtaining accurate and reproducible results. A college-level education with an emphasis on math and science is recommended. After an appropriate training program, continued evaluation and feedback are important. Second, instrument maintenance should be performed on a scheduled basis to reduce or prevent instrument malfunctions. Corrective maintenance, which is usually unscheduled, should be performed by knowledgeable individuals and any repairs should be documented. Third, a procedure manual is very important to any successful quality assurance program. It should contain a broad range of information including administrative issues, quality-control procedures, stepwise instructions on test performance, and infection-control policies and procedures. Fourth, the procedures should be performed using published guidelines to help minimize the effects of the many variables. Fifth, a method to quality control each test procedure should be developed. The specific method(s) will vary according to the type of instrumentation and the manufacturer. Finally, the well-run quality assurance program must properly analyze and store the data collected. Sound statistical methods should be applied and various logs and lists should be developed.