Objective: To evaluate the antimicrobial susceptibility of Gram-negative uropathogens isolated from pregnant women.Methods: We performed a snapshot cohort study of women receiving care in the University of Florida prenatal clinics duringMarch 2000. Subjects with asymptomatic bacteriuria or cystitis were identified and the antimicrobial susceptibility of each pathogen was recorded. Data were analyzed using chi-square, Fisher's exact test and ninety-five percent confidence intervals, as appropriate.Results: Ninety-five positive cultures were identified. Isolates were more often susceptible to trimethoprimsulfamethoxazole (TMP-SMX) (87%) and nitrofurantoin (89%) than to ampicillin (72%) (p < 0.03). Escherichia coli accounted for 71 (75%) cases and was more often susceptible to nitrofurantoin (100%) than to TMP-SMX (87%) (p < 0.01). Proteus isolates were all susceptible to TMP-SMX and resistant to nitrofurantoin (p < 0.01).Conclusions: Both TMP-SMX and nitrofurantoin are superior to ampicillin for empiric treatment of lower urinary tract infection in pregnant women. Nitrofurantoin is superior to TMP-SMX for treatment of infections caused by E. coli. For suspected or confirmed cases caused by Proteus organisms, TMP-SMX is the preferred agent.