The experiments show that 30 virus-induced or virus-specified proteins were synthesized in Raji cells after superinfection with Epstein-Barr virus (EBV) derived from P3HR1 cells. Using a combination of pulse labelling, application of cycloheximide blocks at different times post-infection, treatment with amino acid analogues and inhibition of DNA synthesis it was shown that three groups of proteins appear in Raji cells after superinfection; the synthesis of the proteins in any one group appears to be coordinately regulated. Amongst the six virus-induced proteins which were synthesized immediately after release from an early cycloheximide block one would expect to find those proteins essential for the transition from EBNA to EA synthesis. Using human sera with differing specificities for the various antigen groups 11 proteins were identified as being specifically precipitated by sera having high titres against the EBV-induced early antigen complex.