Telomerase activity was measured with a quantitative assay, based on a modification of telomeric repeat amplification protocol method, in bladder cancers and apparently normal mucosa in 33 patients. In the same patients, the enzyme was also measured in exfoliated cells collected both with voided urine and bladder washings. Results obtained in urine were compared with those from 20 healthy subjects. Telomerase activity was present in 31 (94%) bladder cancer tissues and in 23 (72%) apparently normal mucosa samples. However, the levels of enzyme activity were significantly higher in cancer tissues in comparison with normal mucosa (mean +/- SD, 47.3 +/- 23.2 and 14.9 +/- 6.1 ng DNA/microg protein, respectively; P < 0.0001). Telomerase activity in bladder cancer tissues was not related to tumor stage and grade. Enzyme activity was present in 27 urine samples and in 27 (82%) bladder washings collected from cancer patients. We did not find correlation between the activity in urine and washings, and their mean levels were not different (22.2 +/- 10.1 and 20.7 +/- 8.0, respectively). Telomerase activity in bladder cancer tissues was correlated to its activity in urine (r = 0.650, P < 0.001) and in bladder washings (r = 0.410, P < 0.05). Only 2 of 20 urine samples from control subjects were found to express telomerase activity at a very low level. This was the first attempt to correlate telomerase activity in exfoliated cells from urine and bladder washings with the activity in corresponding bladder cancers. According to these results we postulate that telomerase activity in urine sediment reflects the activity in bladder cancers better than bladder washings and, for its easy collection, is to be preferred as diagnostic marker in this tumor.