Telomerase activity and telomere length were analyzed in a total of 59 surgically removed primary renal cell carcinoma (RCC). The study includes tissue from the centre of the tumor, several different peripheral tumor areas, metastases and secondary tumors. None of the normal renal cortex tissues used as control exhibited telomerase activity. In contrast, telomerase activity was detected in 55 out df 59 (=93%) tested primary RCC. There was no case with intratumoral heterogeneity concerning the telomerase activity status. All metastases and secondary tumors were telomerase-positive. In the four telomerase deficient tumors all measured telomeric repeat fragments were shortened in comparison to the normal tissue. As these patients exhibit no metastases or secondary tumors a less malignant variant of RCC is supposed. There was no correlation between telomerase activity and specific histopathological subtypes of RCC or specific chromosomal aberrations. As telomerase activity is not associated with advanced stages of tumors it may be an important early event in the development of RCC. Thus, telomerase activity may be a prevalent marker for early and late stages of all subtypes of RCC.