Of 210 women who were experiencing dysuria, frequent urination, pyuria, and significant bacteriuria and who were treated with a single 3-g dose of amoxicillin, 165 (79%) were cured of their original infections. Patients with infections that were negative by antibody-coated-bacteria assay were cured at a significantly higher rate than those with infections that were positive by antibody-coated-bacteria assay (90 versus 59%; P less than 0.001). Similarly, those with infections caused by amoxicillin-susceptible organisms were cured at a significantly higher rate than those with infections caused by resistant organisms (85 versus 50%; P less than 0.001). Of 27 patients who had infections caused by amoxicillin-susceptible organisms and who had relapses after single-dose therapy, 14 (52%) had relapses again after a conventional 10-day course of therapy, although all responded to a 6-week course. An additional 27 patients experiencing dysuria, frequent urination, and pyuria but who had a lower number of uropathogens in the urine (10(2) to 10(4.5)/ml of urine) were treated with single-dose therapy, with a 100% eradication of organisms and an 89% rate of symptomatic relief.