This randomized, double-blind, crossover, placebo-controlled study involved 20 incontinent geriatric patients; all had indwelling Foley catheters. Each patient received chlorophyllin 100 mg/d for two weeks and placebo daily for two weeks, separated by a washout period of one week. For each subject, the intensity of urinary odor was measured ten times during both the treatment and placebo regimen and three times during the washout period, using a visual analog scale. A decrease in urinary odor was associated with chlorophyllin in 12 patients and with placebo in 6 patients at the end of two weeks on each regimen. Chlorophyllin treatment was associated with about a 21-percent decrease in mean urinary odor intensity, whereas placebo increased the odor by about 9 percent. The mean intensity of urinary odor was lowest during the second week of chlorophyllin treatment. Despite the decrease in urinary odor in many patients receiving chlorophyllin, its effect was not significantly greater than that of placebo. Our data suggest that chlorophyllin 100 mg/d for two weeks may not be effective in incontinent geriatric patients with mild to moderate urinary odor.