In Vero cells infected with Bunyamwera virus there is a rapid inhibition of cell RNA and protein synthesis to levels of 30 and 3% respectively of the control rate, both the rate of inhibition and the time lag before its initiation being multiplicity dependent. Using u.v.-irradiated virus, investigation of the mechanism of inhibition of host cell protein synthesis indicates that synthesis of new virus components is required for inhibition to occur. Quantitative comparison of the proteins synthesized in infected cells shows that at higher m.o.i. synthesis of virus, as well as cellular proteins, is inhibited. Bunyamwera virus-infected Vero cells synthesized three virus-specific proteins identified as the structural virion proteins. Nucleoprotein is synthesized predominantly early in infection while the major envelope glycoprotein and the minor glycoprotein are synthesized predominantly late in the infection cycle.