Urinary excretion of Tamm-Horsfall protein in women with recurrent urinary tract infections. Since MS-fimbriated bacteria adhere to Tamm-Horsfall protein, it has been suggested that Tamm-Horsfall protein may trap urinary pathogens and prevent them from colonizing the mucosal surfaces of the urinary tract. To test the hypothesis that low urinary Tamm-Horsfall protein excretion rates predispose to urinary tract infection we obtained serial urine samples from 17 women with and 18 without a history of recurrent urinary tract infection. None of the women had known structural abnormalities of the urinary tract. Concentrations of Tamm-Horsfall protein in urine were measured with a sensitive enzyme-linked immunosorbent assay method. On the average, 3 urine samples per person collected within 3 to 6 months were analyzed. The mean Tamm-Horsfall protein excretion of women with recurrent urinary tract infection was 57.0 mg./l. and that of controls was 66.3 mg./l.; this difference was not statistically significant. The mean coefficient of variation was 44.2 and 62.1%, respectively. We conclude that urinary Tamm-Horsfall protein concentration is not significantly decreased in women with recurrent urinary tract infection compared with controls, and that excretion varies widely in repeat samples obtained from the same individual. 