To identify a suitable test for mass detection of significant bacteriuria, urine specimens from apparently healthy women were studied by culture, species identification, and colony count with two microscopic stained urine-droplet techniques and with triphenyltetrazolium chloride (TTC) in two forms—a commercially prepared powder and a fresh, homemade solution. Triphenyltetrazolium chloride testing in either form was simpler than microscopic methods and a more sensitive detector of pathogenic orgonisms in numbers exceeding 105/ml. Commercial TTC was sensitive at times, but unreliable. Fresh preparation, incubated with urine for six hours at 37C, was highly sensitive, specific, and reliable, with desirably low contaminant detection rate. In duplicate studies, results with this technique were at least as reproducible as those of culture and colony count. This simple, inexpensive method appears to be the most useful one currently available for screening.