Routine urinalysis is performed as a screening test for urinary tract infection (UTI) in out-patients or in-patients. We assessed the usefulness of microscopic examination of unspun and unstained urine using a disposable slide with counting chambers (Kova Slide 10 grid, Miles-Sankyo) for diagnosis of significant bacteriuria. 173 fresh urine samples were obtained from 173 subjects (89 male and 84 (female), including 117 inpatients, aged from 0 to 96 years. Urine samples were examined for bacteriuria by the standard culture method and counting chamber method. Significant bacteriuria was defined as 10(5)/ml or more of bacilli for midstream urine and urine collected by bags and 10(4)/ml or more for urine collected by catheterization and from indwelling catheters. Urine leukocytes were also counted on disposable slide. The rapid dipstick test (N-multistix-SG-10, Miles-Sankyo) of leukocyte esterase activity and nitrite were measured in the urine specimens read by a photometer (Clinitek-10, Miles-Sankyo). Significant bacteriuria was diagnosed by standard culture method in 67 urine samples. Close correlation was obtained between bacterial counts determined by the bacterial culture and counting chamber method (Spearman's correlation coefficient p < 0.001). Sensitivity and negative predictive value for significant bacteriuria were 94.0 and 95.1%, respectively, when bacteriuria or pyuria was present in the counting chamber. Dipstick test had a sensitivity and negative predictive value of 86.6 and 89.9%, respectively, when either leukocyte esterase activity of + or more, or nitrite of + was found. In out-patients, both sensitivity and negative predictive value were as high as 100% in counting chamber method. Thus, we can conclude that urine microscopy on disposable counting chambers is a very sensitive, simple, time-saving and lost-effective method for diagnosis of UTI.