The pre- and post-treatment urinary total sialic acid/creatinine (TSA/Cr) ratios of patients with bladder tumor (n = 60) were determined. We found a significant increase in the mean urinary TSA/Cr ratio in patients with bladder tumors than in healthy people (99.80 +/- 15.60 mu g/g Cr, 52.57 +/- 15.60 mu g/g Cr, P < 0.001). We determined that the mean post-treatment TSA/Cr ratio of 44 patients was significantly lower than their pretreatment ratio and this value also decreased to the level in healthy people. (TSA/Cr ratios of 44 patients: in the pre-treatment period, 105.30 +/- 25.20 mu g/g Cr; in the post-treatment period, 54.50 +/- 15.80 mu g/Cr; healthy people, 52.57 +/- 15.60 mu g/g Cr, P < 0.001). The patients with decreased TSA/Cr ratio in the post-treatment period showed complete or partial regression of their disease. In 8 patients, urinary TSA/Cr ratio in the post-treatment period increased to 105 +/- 14.5 mu g/g Cr value. In clinical and pathologic evaluation, it was shown that disease progressed in all of these 8 patients. The mean post-treatment TAS/Cr ratio of 8 patients did not differ from the pretreatment ratio (87.44 +/- 20.20 mu g/g Cr) and it was shown that their clinical status did not change. These findings show that urinary excretion of TSA correlates with the clinical status of bladder tumor and it could be used to follow the course of the disease, and follow-up treatment.