The presence of significant pyuria (≥ 8-10 leukocytes/mm3) is one of the most important indicators of a urinary tract infection. Pyuria can be determined by direct microscopy, hemocytometry, or a rapid diagnostic assay. The determination of bacteriuria as measured by microscopy or rapid detection methods is a less reliable indicator of infection. Quantitative urine cultures are the best measure of bacteriuria, and significant growth may be as low as 102 CFU/ml for women with acute dysuria as opposed to the old standard of ≥ 105 CFU/ml. This article reviews the utility of these and other tests in the diagnosis, localization, and management of urinary tract infections.