Many drugs have been reported to interfere with copper-reduction or glucose oxidase tests used to measure urine glucose. However, only a few drugs or drug classes have been well documented to clinically interfere with these tests. The interfering drugs include ascorbic acid, beta-lactam antibiotics (e.g., cephalosporins and penicillins), levodopa, and salicylates. Several other drugs may also interfere with certain urine glucose tests, but the interactions are poorly documented. These drugs include chloral hydrate, hyaluronidase, nalidixic acid, nitrofurantoin, p-aminosalicylic acid, phenazopyridine, probenecid, and X-ray contrast media. Drugs or their metabolites that are strong reducing substances produce false-positive results by the copper-reduction method and false-negative results by the glucose oxidase method. The beta-lactam antibiotics interfere with copper-reduction tests by producing copper compounds of various colors that confuse interpretation of test results. Tables are provided that summarize the drug interferences discussed.