The value of the differential leukocyte count in case finding in the ambulatory care setting was evaluated by retrospectively reviewing 799 encounters resulting in complete blood cell counts. Four hundred seventy-five differential leukocyte counts, of which 63 were abnormal, met criteria for case finding. No clinically inapparent disease was discovered through the use of these tests. These data suggest that the quantitative cell counts of the differential leukocyte examination may be of no value in case finding in the ambulatory care setting.