The chemopreventive efficacy of cranberry juice concentrate in an experimental model of urinary bladder cancer was evaluated using female Fischer-344 rats. The animals received N-butyl-N-(4-hydroxybutyl)-nitrosamine (OH-BBN) for a period of eight weeks. Cranberry juice concentrate was administered at doses of 1.0 or 0.5 ml/rat/day beginning one week after the final OH-BBN treatment and continuing until the end of the study. The urinary bladders of all the rats were weighed and examined grossly for lesions, and all masses were submitted for pathological evaluation. A dose-dependent preventive effect of cranberry treatment was observed, with a reduced number of urinary bladder cancers (38%) in the 1.0 ml/rat/day group versus the control group. The cranberry extract neither affected body weight gain nor caused other signs of toxicity. For the metabolic studies, serum and urine were collected at 4 and 12 h after the administration of the cranberry juice concentrate and were analyzed by LC-MS/MS. Quercetin and its methylated derivative were detected in the urine samples. However, no quercetin was detected in the serum samples, indicating its poor bioavailability. These data suggest that components of cranberries may be effective in preventing urinary bladder carcinogenesis.