The pre-1990 College of American Pathologists' (CAP) Proficiency Testing (PT) program used a two samples per analyte/four challenges per year format with performance or pass-fail grading criteria determined by the program. On Jan. 1, 1991, the Clinical Laboratory Improvement Act of 1967 (CLIA-67) final rules (March 14, 1990) mandated a revised PT format of five samples per analyte/four challenges per year, with the regulations specifying minimum performance criteria. Extending our previous analysis, we compare the maximum permissible intralaboratory imprecision at low bias compatible with passing external PT in the former CAP and current CLIA-67 formats. If a laboratory is able to reduce its internal coefficient of variation (CV) to less than 44% of the PT criterion for each analyte, its overall chance of adverse action for any of the 27 routine chemistry analytes specified in CLIA-67 will be less than 1% in a two-year (eight PT challenges or events) period. Consideration of actual interlaboratory CVs from CAP surveys suggest that a reduction of this magnitude may be difficult for the analytes total cholesterol and blood urea nitrogen, where intralaboratory imprecision comparable with the group standard deviation (SD) from 1990 CAP surveys would yield individual adverse action (PT failure) rates of 5% and 1%, respectively. Five other analytes have CLIA-67 performance limits dangerously close to CAP interlaboratory CVs.