A series of consecutive urine cultures was performed to determine the time points of elimination of bacteria from urine and the factors influencing these time points in patients receiving antimicrobial chemotherapy for positive bacteriuria. Between 1988 and 2000, 110 patients who had positive bacteriuria and received a 5-day regimen of parenteral antibacterials were included in this study. Quantitative urine cultures were performed every 24 h throughout the therapy. Bacteria were identified; minimum inhibitory concentrations of antibacterial agents for causative bacteria were determined, and the bacteria were categorized as susceptible or nonsusceptible. The complexity of the urinary tract was graded as high or low. A multivariate Cox proportional hazards model was utilized to identify the factors that determined the time course of bacterial density in urine. Two penicillins, seven cephalosporins, five carbapenems and one fluoroquinolone were administered to 110 patients. The overall bacteriurial elimination rate at the end of treatment was 73% (80/110), and the most frequent day of elimination was day 1 (54%; 43/80), followed by day 2 (20%; 16/80). The significant factors for persistence of bacteriuria after chemotherapy were the presence of an indwelling catheter, a nonsusceptible pathogen, and high complexity of the urinary tract; risk ratios were: 2.398 (P = 0.0009), 2.227 (P = 0.0020), and 2.113 (P = 0.0455), respectively, which also influenced the day of elimination. In conclusion, the efficacy of treatment and the time point of bacteriurial elimination were determined by the presence of a urinary catheter, drug susceptibility, and urinary complexity in patients with positive bacteriuria undergoing antibacterial chemotherapy.