We report the case of an 81-year-old female patient with diverticulitis of the colon, whose symptoms were relieved by intravenous administration of cefpirome. However, her serum creatinine levels were falsely increased by the Jaffe method when serum samples were drawn after intravenous administration of cefpirome. The serum creatinine level in the same sample was within the normal range by the enzymatic method in the automated analyzer. In vitro experiment demonstrated dose-dependent positive interference of the creatinine level with cefpirome. These results indicate that we should be aware of the positive interfering effect of cefpirome when we measure serum creatinine by the Jaffe method, and that the enzymatic method should be widely used to measure serum creatinine levels to eliminate false reactions due to certain chemicals.