A photometric method which detects bacterial multiplication in urine is described. The apparatus is both inexpensive and easy to use, and results are obtained within four hours. A total of 217 urine specimens from 181 patients were assessed and the results compared with the corresponding laboratory tests, which showed a significant growth in 102 specimens. The sensitivity and specificity of the photometric method was 77% and 99%, respectively, with a positive accuracy of 99%. The photometer detected 83% of significant enterobacterial infections and 76% of mixed infections. It is suggested the false negative results (23%) may have included high laboratory colony counts not associated with active urinary tract infection.