In this study, we have identified an internal ribosome entry site (IRES) from the highly infectious herpesvirus Marek's disease virus (MDV). The IRES was mapped to the intercistronic region (ICR) of a bicistronic mRNA that we cloned from the MDV-transformed CD4(+) T-cell line MSB-1. The transcript is a member of a family of mRNAs expressed as immediate-early genes with two open reading frames (ORF). The first ORF encodes a 14-kDa polypeptide with two N-terminal splice variants, whereas the second ORF is contained entirely within a single exon and encodes a 12-kDa protein also known as RLORF9. We have shown that the ICR that separates the two ORFs functions as an IRES that controls the translation of RLORF9 when cap-dependent translation is inhibited. Deletion analysis revealed that there are two potential IRES elements within the ICR. Reverse genetic experiments with the oncogenic strain of MDV type 1 indicated that deletion of IRES-controlled RLORF9 does not significantly affect viral replication or MDV-induced mortality.