A study was conducted to evaluate the ability of a urine filtration system (Bac-T-Screen, Marion Laboratories, Inc., Kansas City, Mo.) to detect negative urine cultures within 2 min. A total of 1,000 urine specimens were tested with the Bac-T-Screen and compared with a standard semiquantitative culture plate method and the Autobac system (General Diagnostics, Warner-Lambert Co., Morris Plains, N.J.). Of the 1,000 clean voided urine specimens tested, 246 specimens had colony counts greater than or equal to 10(5) CFU/ml by the culture plate method. Of these, the Bac-T-Screen detected 65.4% (161 of 246), and the Autobac detected 63.0% (155 of 246). When pure cultures of diphtheroids, lactobacilli, and viridans streptococci other than group D and cultures containing multiple organisms were considered to be contaminants and, therefore, were excluded, there were 106 pure cultures of probable pathogens of which the Bac-T-Screen detected 76.4% (81 of 106) and the Autobac detected 90.6% (96 of 106). Some 133 specimens were uninterpretable with the Bac-T-Screen because 36 clogged the filter and 97 left a residual pigment on the filter. A majority of those clogging the filter (69.4%) had positive plate counts, whereas the majority of the pigmented urines had negative plate counts. Of those urine specimens tested. 754 were negative by the culture plate method. The false-positive rates for Bac-T-Screen and Autobac were 16.2 and 5.8%, respectively. As a urine screen, the Bac-T-Screen has a negative predictive value comparable to the Autobac system and has the advantage of being a 2-min test.