The method developed for establishing a blind proficiency testing (PT) system is presented. The Laboratory Assurance Program of the Graduate School of Public Health at San Diego State University is developing and pilot testing innovative strategies that will evaluate and improve the performance of clinical laboratories. To date, a total of 32 laboratories have been incorporated into this program along with 12 counseling and testing sites. From June 1988 to December 1989, five blind PT surveys for human immunodeficiency virus type 1 antibody testing were conducted, representing 306 proficiency specimens entered into the testing system as simulated patient specimens. Despite the difficulties and expense involved, we found the system to be acceptable and to have certain advantages over conventional methods of external testing.