Ribosome binding to cellular eukaryotic mRNAs is proposed to occur by initial attachment at or near the mRNA 5' cap structure (m7 GppN, where N is any nucleotide) followed by scanning till the appropriate initiator AUG is encountered. A pivotal aspect of this model is the obligatory entry of the ribosomes at the 5' end of the mRNA (regardless if it contains a cap structure). Recent experiments, however, demonstrated that ribosomes can access certain mRNAs by internal binding to the 5'-untranslated region. This was most clearly demonstrated for members of the picornavirus family such as poliovirus and encephalomyocarditis virus. Further experiments suggest that other viral mRNAs and even cellular mRNAs may use similar mechanisms of ribosome binding. Here we describe some features of the poliovirus 5'-untranslated region and possible trans-acting factors that are involved in this mechanism of translation.