Microstix is a simple and convenient reagent strip for obtaining a semi-quantitative bacterial count on urine specimens. This method correctly predicted over 10(5) gram-negative organisms per ml in 84 percent of samples and over 10(5) gram-positive organisms per ml in 72 percent. Urine specimens containing 10(4) per ml or more of any organism should be recultured using fully quantitative methods. If this criterion had been used 89 percent of urine samples with over 10(5) organisms per ml would have been detected with Microstix and only 33 of the 393 remaining samples would need to have been repeated. The false positive rate was low. This method would be ideal for use in doctors' offices to culture the urine of patients presenting with urinary tract symptoms. It would also be very suitable for use in hospital clinics and for the screening of asymptomatic populations who are high risk of having urinary tract infections.