A total of 221 elderly patients between the ages of 70 to 99 years who presented to a community-based teaching hospital emergency room were prospectively evaluated by assessing for fever (greater than or equal to 37.5 degrees C), leukocytosis (greater than or equal to 14,000/mm3) and bandemia (greater than 6%) as a screening method for predicting the presence of bacterial infection. Thirty-three patients had documented bacterial infections. Although with increasing body temperature the percent of patients who were infected increased, 48% of the infected elderly patients had no fever. In patients with fever, 39% had a bacterial infection compared to only 9% in the afebrile group. In patients with fever, leukocytosis, and bandemia, all patients were infected. Conversely, in the absence of fever, leukocytosis, and bandemia, only 6% had bacterial infection. All elderly patients who present with an acute or subacute change in health status or functional capabilities associated with fever, leukocytosis, or bandemia should be carefully assessed for the high probability of a bacterial infection.