Coronaviruses are species specific and cause mainly respiratory diseases in humans, in part because cells of the respiratory tract express receptors allowing them to attach and infect. While the A59 strain of mouse hepatitis virus (MHV-A59) only infects mouse cells, not cells from other animals, cultures of mouse cells persistently infected with MHV-A59 for 23-600 passages produce virus (pi23-pi600) that is no longer species specific. Loss of species specificity was controlled by changes in the viral genome since a recombinant virus (MHV-rec2A) obtained from cells coinfected with MHV-A59 and pi600 had properties of both viruses and grew in mouse, rat, hamster, monkey and human cells. We wanted to know if this virus used the same receptor or co-receptor to enter cells and used the same entry pathway as MHV-A59. Bgb-1 and -2 are receptors for MHV-A59. BHK cells were not susceptible to infection by MHV-A59 but bound similar amounts of virus as mouse cells, suggesting the block to infection occurred after binding. Infection steps after binding include internalization by membrane fusion that may require a co-receptor and uncoating of the viral genome RNA, followed by its translation and transcription. Pretreatment of cells with DEAE-dextran altered infection efficiency: the number of cells infected by MHV-A59 increased 5-10 folds after pretreatment, whereas that of MHV-rec2A decreased 3 folds. The increase in MHV-A59 did not result from an increase in virus binding or internalization but pretreated cells showed earlier viral RNA synthesis and progeny virus production, consistent with the entry of more genomes. Confirming this hypothesis, decreasing the number of virus particles used for infection restored normal RNA synthesis. In contrast, pretreatment delayed MHV-rec2A RNA synthesis and virus production and this delay in entry was not overcome by infecting with more virus. Our results suggest that DEAE-dextran affects entry at a post-binding step. We also argue that loss of species specificity by MHV-rec2A results from its ability to use a different entry pathway than MHV-A59.