Hepatitis A virus was purified from the feces of 2 patients with unrelated, naturally acquired infections and was inoculated into FRhK-4 cells. Analysis of protein synthesis by double-label coelectrophoresis and subtraction allowed the resolution of virus-specific proteins synthesized during infection. In FRhK-4 cells the two strains of virus studied produced markedly different profiles of virus-specified proteins, with an accumulation of high-molecular-weight proteins for strain HM790 relative to strain HM175, suggesting a level of restriction in the processing of the viral polyprotein.