The effect of the new antibiotics imipenem-cilastatin and ciprofloxacin on the accuracy of tests for glycosuria was studied. Samples of urine from two healthy volunteers were used to prepare solutions containing various concentrations of glucose and drug. Glucose concentrations were tested in triplicate by the Clinitest, Tes-Tape, and Diastix methods. As controls, samples of urine containing the antibiotics alone or various concentrations of glucose and cefazolin were tested by each of the three methods. Low concentrations of imipenem-cilastatin caused falsely low glucose results in urine samples containing 0.5% and 1% glucose analyzed by the Clinitest method. Ciprofloxacin did not interfere with determination of urine glucose concentration by the Clinitest method at any of the drug concentrations tested. Neither of the antibiotics interfered substantially with determination of urine glucose concentration by the Diastix or Tes-Tape methods regardless of the concentration of glucose or drug. At the concentrations tested, ciprofloxacin did not interfere with determination of urine glucose concentration by the Clinitest, Diastin, or Tes-Tape methods. Although imipenem-cilastatin may produce falsely low glucose measurements with the Clinitest method, this interaction is not of great clinical importance.