The effect of D-mannose and D-glucose on bacteriuria due to Escherichia coli with mannose-sensitive adhesins was investigated in adult male Sprague-Dawley rats undergoing diuresis. Inocula of 10(5), 10(7), or 10(8) bacteria in 0.1 ml of normal saline or 2.5% or 10% D-mannose or D-glucose were injected intravesically and urine was cultured 1, 3, 5, 7 and 9 days later. The levels of bacteriuria on days 1 and 5 were significantly lower in rats inoculated with 10(5) E coli and 10% D-mannose than in controls (p less than 0.05 and 0.01 respectively) and the percentages of rats with less than 100 bacteria/ml were higher on days 1 and 3 (p = 0.05 and 0.02 respectively). Bacteriuria was significantly lower in rats inoculated with 10(7) bacteria and 10% D-mannose than in controls on days 5 and 7 (p less than 0.01 for each day) and the percentage of rats with less than 100 bacteria/ml was higher on day 7 (p = 0.01). D-glucose reduced bacteriuria significantly only with a concentration of 10% after instillation of 10(5) E. coli (p less than 0.05, day 1). The results indicate that D-mannose and D-glucose can significantly reduce bacteriuria within 1 day and that their efficacy is dependent upon the concentration of both saccharide and bacteria.