The authors compared dipstick tests for leukocyte esterase and nitrite and microscopic examination of urinary sediment with urine culture to assess whether the former tests could reliably rule out bacteriuria in specimens from children. The authors studied urine specimens from 1010 infants and children younger than age 18. Compared with culture at greater than or equal to 10(5) colony forming units (cfu)/ml, the sensitivities of leukocyte esterase, nitrite, and microscopic examination of white blood cells (greater than or equal to 5 wbc/hpf) or bacteria (in at least moderate numbers) were 76 percent, 29 percent, 82 percent, and 80 percent, respectively. The specificities of the same tests were 81 percent, 99 percent, 81 percent, and 83 percent, respectively. Compared with culture at greater than or equal to 10(4) cfu/ml, the sensitivities of the tests were 64 percent, 21 percent, 64 percent, and 59 percent; the specificities were 82 percent, 99 percent, 81 percent, and 83 percent, respectively. The negative predictive values of leukocyte esterase and microscopic examinations of urinary sediment for white blood cells and bacteria were all 95 percent (greater than or equal to 10(4) cfu/ml) or 98 percent (greater than or equal to 10(5) cfu/ml). The authors conclude that the leukocyte esterase test is as accurate as sediment microscopy in identifying urine specimens from infants and children harboring less than 10(4) or less than 10(5) cfu/ml.