AbstractSurvivin, a novel member of the inhibitor of apoptosis protein (IAP) family, reduces the susceptibility of tumor cells to proapoptotic stimuli, thereby promoting tumor cell survival during tumor progression and treatment with anticancer drugs. Recently, we identified 2 novel alternative splice variants of survivin, survivin‐2B and survivin‐ΔEx3, which differ in their antiapoptotic properties. Survivin‐2B has lost its antiapoptotic potential and may act as a naturally occurring antagonist of antiapoptotic survivin and survivin‐ΔEx3. Because the in vivo expression of these splice variants in human cancer has not been analyzed so far, 57 renal cell carcinomas (RCCs) were explored using quantitative reverse transcriptase polymerase chain reaction. We found that all RCCs express survivin‐ΔEx3, survivin‐2B and survivin, the latter being the dominant transcript. When we compared early and intermediate stages with late stages of clear cell RCCs, no significant changes in the expression levels of survivin and survivin‐ΔEx3 became evident. However, a significant decrease was observed for the mRNA ratio between survivin‐2B and survivin in late tumor stages (p = 0.036). Chromophilic/papillary RCCs, which are known to be less aggressive than clear cell RCCs, did not show significantly lower expression levels of antiapoptotic survivin and survivin‐ΔEx3, compared with stage‐adjusted clear cell RCCs. Our study demonstrates for the first time in vivo expression of functionally different survivin variants and suggests a role of these survivin splice variants in the progression and clinical behavior of human RCCs. © 2002 Wiley‐Liss, Inc.