The polypeptides present in BHK21 cells infected with aphthovirus C2 and harvested at different intervals post infection were studied by immunodiffusion, immunofluorescence, electrophoresis in polyacrylamide gel and radioactive profiles. The possible relationship with the induction of protecting antibodies produced by rabbits was also studied. The radioactive profiles were different for each sample. Fluorescence was observed at 65 minutes post infection and morphologic changes and alterations in the cells due to viral cytopathic effect were observed 120 minutes post infection. Our results indicate that: unreleased or penetrating virus is present 75 minutes post infection; early viral progeny with possible prelytic liberation are present between 75 and 120 minutes post infection; the formation and liberation of viral progeny occur after 120 minutes post infection. In a previous publication we showed that cells after 75, 120 and 210 minutes of infection induced the production of neutralizing antibodies in rabbits. Correlating these results with the ones presented here in, we postulate that the responsibility in production of neutralizing antibodies would depend on precursors of structural polypeptides rather than on the latter.