The usefulness of three components of the routine admission complete blood cell count (leukocyte count, hematocrit, and platelet count) was evaluated in 301 patients consecutively admitted to the internal medicine wards of a university teaching hospital. Using a consensus analysis approach, three faculty members reviewed the patients' charts to determine which tests were performed routinely, which tests were abnormal, and which routine tests led to diagnostic or therapeutic changes. Overall, 55.3% of the tests were considered routine admission tests. Abnormalities were detected in 13.6% of the routine leukocyte counts, in 8.2% of the routine hematocrit levels, and in 12.4% of the routine platelet counts. However, treatment was changed for only three patients, all of whom had low hematocrits; this amounted to 0.6% of all tests. Furthermore, only one of the three patients received appropriate treatment that might have been withheld if a routine hematocrit determination had not been ordered. The authors conclude that the impact of routine admission complete blood cell counts on patient management is small and that the practice of ordering this test for all hospitalized patients could be eliminated with little adverse effect on patient care.