A sensitive, simple and rapid method for detection of bacteriuria has been developed. By means of a Luminol chemiluminescence method adapted to an Auto Analyzer it has been possible to indicate the presence of low concentrations of bacteria in urine specimens from an unselected clinical material. Less than 1 per cent of the investigated urine samples were false negatives and 7 per cent were false positives according to the Luminol method as compared with viable count. Blood is a disturbing factor. No special treatment of the specimens of urine was needed. The analysing time was only two minutes. Formaldehyde could be added without interfering with the analysis. As the reagents required are inexpensive, and with autoanalyzers available at many hospitals, the Luminol method might be of interest as a mass screening technique for bacteriuria.