The uptake and persistence of 3-methylcholanthrene have been followed in both unifected rat embryo tissue culture cells and in cells infected with type C RNA virus. No significant differences in these parameters were observed as a function of viral infection or cell passage level. Moreover, neither binding of 3-methylcholanthrene to nucleic acids or proteins nor carcinogen metabolism were altered by the viral carrier state. Although transformation of rat cells by chemical carcinogens alone has been reported by us and other authors, the low-passage rat embryo cells used in this study will not transform unless cells are carrying exogenous type C RNA virus. We thus suggest that the virus must play a more direct role in the transformation process rather than affecting the ability of the cell to absorb, retain, or metabolize the chemical.