Large-scale purification of rubella virus from tissue culture fluid and preparation of an experimental rubella subunit vaccine are described. The virus, purified isopycnically in sucrose gradients, was Tween 80-ether treated, and the product was filtered sterile. The vaccines were of two types, formalinized and nonformalinized. They were not infectious, had only a slight pyrogenicity, and caused no harmful symptoms in animals. The immune response in guinea pigs was better when the nonformalinized vaccine was used and the dosage was 2,500 hemagglutinating units per injection (0.5 ml). "Live" attenuated virus vaccines have been de-tures (28). The virus-containing medium was clarified veloped for the prophylaxis of rubella, and large-by low-speed centrifugation, its pH was adjusted to scale vaccinations have been started in several 7.3 with NaHCO3, and it was either frozen rapidly countries. These vaccines give a good serocon-to-70 C for storage or immediately processed. version rate and protect the vaccinee against the Hemagglutination (HA) and plaque assay in BHK-21/WI-2 cells and preparation of electron micrographs clnical disease. But the vaccinees may become have been described earlier (28), as has the treatment reinfected without clinical symptoms; they then with Tween 80 and ether (26). excrete the vaccine virus from the respiratory Continuous-flow rotor B-XVI. Initially we had some tract and may even cause the transmission of difficulties in operating the rotor because of incomplete vaccine virus to a susceptible contact (12, 14, 19, information from the manufacturer, Beckman Instru-23, 27). In addition, rubella vaccine virus has been ments, Inc., Spinco Division, Palo Alto, Calif. A recovered from the uterine cervix and the products major problem was the original upper seal housing, of conception (22, 27). which was not designed to stand the high velocity of Only a few attempts to develop "killed" rubella the rotor and its resonance vibrations. Thus, one of virus vaccines have been made. Some of the the primary demands was the adjustable seal housing