Incubation of HeLa cells at supraoptimal temperatures induces the synthesis of a class of proteins known as heat-shock or stress-response proteins. After restoration of cells to physiological temperatures heat-shock protein synthesis continues for several hours. Normal cellular translation eventually recovers even if cells are treated with actinomycin D, indicating that neither normal cellular mRNAs nor components of the translation machinery are irreversibly modified by heat treatment. The synthesis of heat-shock proteins after poliovirus infection is more resistant to inhibition than normal host proteins. Nevertheless, their synthesis is also inhibited in infected cells, even in cells treated with human interferon under which conditions viral RNA replication and viral translation are blocked. Translation of heat-shock proteins is also resistant to hypertonic shock indicating that their mRNAs bind ribosomes with high affinity.