This study examined telomerase activity and gene expression profiles for three genes in Gallus gallus domesticus: telomerase reverse transcriptase (chTERT), telomerase RNA (chTR), and c-myc. Expression of these genes was studied in chicken embryonic stem (chES) cells, chicken embryo fibroblasts (CEFs), and DT40 cells using quantitative real-time polymerase chain reaction. Our results establish that, relative to transcription levels in telomerase-negative CEFs, chTERT and chTR are up-regulated in telomerase-positive chES cells. Transcription levels of chTERT, chTR, and c-myc are dramatically up-regulated in telomerase-positive DT40 cells, relative to CEFs and chES cells. These results are consistent with a model in which telomerase activity is up-regulated in proliferating embryonic stem cells requiring stable telomeres to endure multiple rounds of cell division; down-regulated in differentiated, lifespan-limited cells; and dramatically up-regulated in immortalized, transformed cells for which uncontrolled proliferation is correlated with c-myc dysregulation and telomerase activity.