A continuously growing immortal cell substrate can be used for virus propagation, diagnostic purposes, and vaccine production. The aim of this study was to develop an immortal chicken cell line for efficient propagation of avian infectious viruses. From the various chicken embryo cells that were tested for life span extension, an immortalized chicken embryo liver (CEL) cell line, named CEL-im, was derived spontaneously without either oncogenic viruses or carcinogenic chemical treatment. Currently, CEL-im cells are growing 0.8 to 1.1 population doublings per day and have reached 120 passages. The CEL-im cell line is permissive for poultry infectious viruses, including avian metapneumovirus (AMPV), Marek's disease virus serotype 1 (MDV-1), and infectious laryngotracheitis virus. The CEL-im cells produced high AMPV titer (>10(5) pfu/mL), whereas very low titers (~10 pfu/mL) for MDV-1 and infectious laryngotracheitis virus were produced. To identify genetic alterations in the immortal CEL-im cell line, telomerase activity and mRNA expression for major cell cycle regulatory genes were determined during the immortalizing process. The CEL-im cell line has negative telomerase activity, and when compared with the primary passage 2 CEL cell counterpart, mRNA expression of tumor suppressor protein p53, mouse double minute 2 (Mdm2), cyclin dependent kinase (CDK) inhibitor p21 (p21(WAF)), and CDK inhibitor p16 (p16(INK4)) were downregulated in the CEL-im cell line, whereas retinoblastoma (Rb), transcription factor E2F, member 1 (E2F-1), and alternative reading frame of p16(INK4) (ARF) were upregulated. These results are similar to genetic alterations found previously in immortal chicken embryo fibroblast (CEF) cell lines that showed efficient propagation of MDV-1. Therefore, this newly established CEL-im cell line can serve as an alternative cell substrate for the propagation of poultry viruses, such as AMPV.