To assess the degree to which routine stool cultures, ova and parasite examinations, and Clostridium difficile toxin assays may be inappropriately ordered on hospitalized patients, we conducted a retrospective study to determine the relative yield of these tests on specimens collected from outpatients and inpatients as a function of time after admission. During a 3-year period, only 1 of 191 positive stool cultures and none of the 90 ova and parasite examinations with positive results were from the group of patients who had stool specimens submitted after 3 days of hospitalization. Analysis of laboratory work load for a 1-year period showed that specimens from this patient group contributed nearly 50% of the more than 3000 specimens received each year. In contrast, approximately 25% (range, 17% to 33%) of samples, regardless of admission status, were positive for C difficile toxin. Eliminating routine stool cultures and ova and parasite examinations on hospitalized patients would significantly reduce hospital and patient costs without altering patient care. Nationwide, such a policy might achieve a cost savings of $20 to $30 million per year.