Intracellular virus-specific proteins induced by equine arteritis virus (EAV) have been compared with in vitro translation products of virion and intracellular EAV RNAs. In infected BHK-21 cells, the two major virion proteins (C and E1) and polypeptides with mol. wt. of 60,000 (p60), 42,000 (p42) and 30,000 (p30) were found. There were no indications that the viral proteins were processed from a larger precursor as shown by pulse-chase, amino acid analogue and protease inhibitor experiments. The six polyadenylated RNAs that occur in EAV-infected cells were isolated and translated in an mRNA-dependent reticulocyte cell-free system. Translation of RNA6 resulted in the appearance of a product having the mol. wt. (14,000) of the nucleocapsid protein (C). EAV genomic RNA was translated into proteins of mol. wt. 30,000 and 200,000, while RNA1, the intracellular homologue of genomic RNA only encoded p30. The absence of large precursor molecules in infected cells and the results from the in vitro translation experiments both suggest that at least some of the proteins are primary translation products.