Abstract
SV40 stocks prepared by successive undiluted passages in African green monkey kidney (GMK) cells contain particles which produce T antigen but not capsid antigen (T particles). The DNA of the T particles was shown to replicate during abortive infection of GMK cells, as indicated by immunofluorescence assay for antigen forming capacity of virus DNA. It was also shown that the synthesis of T particle DNA was induced in heterokaryons formed by fusion of 3T3 cells transformed by T particles with susceptible GMK cells.