Using the sensitive telomeric repeat amplification protocol assay, we detected telomerase activity in 26 of 35 (74.3%) renal cell carcinomas analyzed. Subdivision of the tumors according to telomerase activity did not reveal an obvious association between the presence of telomerase activity and histomorphological stage, grade, tumor size, or DNA ploidy. Furthermore, no association was found between telomerase activity and a distinct chromosomal aberration pattern; namely, loss of genetic material on the short arm of chromosome 3. Telomerase activity was also detected in 6 of 35 (17.1%) normal corresponding renal tissue samples, which seems interesting in light of the supposed biological role of telomerase expression in carcinogenesis. Interestingly, telomerase activity was detected in three of the four (75%) kidneys bearing non-clear cell tumor types, whereas of the 31 kidneys with clear cell carcinomas, telomerase activity was found in only 3 (9.7%) normal tissue samples. In addition, the two renal angiomyolipomas and one of the two analyzed transitional cell carcinomas of the renal pelvis were telomerase negative.