THE differing localization and aspects of the teratogenic action of rubella virus reflect different sequelae of the interaction of virus and cells. We have explored the action of rubella virus on the division of human embryonic cells grown in vitro. These studies were initiated at the Wistar Institute with Boué and Plotkin,1,2 and the preliminary results were presented in February 1964.3 It was found that these rubella-virus and some of the human-cell preparations were contaminated with pleuropneumonia-like organisms (PPLO). This work was completed in our laboratory in Paris with rubella virus stocks and human cell lines free of PPLO. The assays confirmed the preliminary results. In spite of rubella virus replication, no cytopathic effect was detected in human cells infected in vitro.4 These results have been confirmed by the observations of Rawls and Melnick5 made in cell lines carrying rubella virus and derived postmortem from infants