In an attempt to reduce clinical laboratory testing, a strategy was designed for a clinician-oriented restriction policy imposed on the laboratory test-ordering mechanism. The program examined the requirement of a written justification to accompany test requests. Directed justification, where specified conditions were required for test performance, was applied to the prothrombin and partial thromboplastin times and resulted in a mean reduction of 44% (P less than 0.001) in these tests; a nonspecific justification directive for leukocyte differentials, where any clinical condition listed generated the test, reduced differentials 35% (P less than 0.001). The justification policy then was extended more broadly and applied on a trial basis to general medical wards. Although no review was made on validity of listed test rationalizations, the justification process alone significantly reduced four common laboratory tests from 28% (BUN/creatinine) to 45% (electrolytes); significant reductions were not seen in less frequently ordered tests. The authors concluded that the most common clinical laboratory tests may be reduced by demanding that the clinician perform a clerical justification when requesting these tests. This mild restrictive policy in the ordering process allows the clinician to maintain responsibility over laboratory testing, while effectively reducing laboratory volume.