Infection of HeLa cells by poliovirus results in the inhibition of translation of capped cellular mRNA. A plausible mechanism for this inhibition is that the structure of one or more initiation factors involved in the recognition of capped mRNA is altered. Eukaryotic initiation factor (eIF) 4A and eIF-4B are implicated in mRNA binding to 40 S ribosomal subunits and can be cross-linked to oxidized capped mRNA. We examined these factors in HeLa cell lysates by two-dimensional isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. No alterations in the number of molecules/cell, in the molecular size, or in extents of covalent modification were detected when lysates from infected and mock-infected cells were compared. The integrity of eIF-2 and several eIF-3 polypeptides was also examined and likewise no alterations were detected. The failure of the translational machinery to recognize capped mRNA therefore is not due to a change in the structure of these initiation factors.