The preparation of inactivated polio and rabies vaccine in tissue culture has been developed into a "Unit Process" at our laboratory during recent years. The process comprises trypsinization of animal kidney cells by the perfusion method, cell/virus cultivation in microcarrier culture and concentration and purification of the virus suspension followed by inactivation. Also, the control tests on the virus suspensions and vaccines are performed, to the greatest possible extent, according to the same procedures. In the meantime, both vaccines thus prepared have been tested in man. High antibody titres have been obtained and no adverse reactions have been observed. The results of a field trial with inactivated poliovaccine, administered at different concentrations, will be presented by Dr Salk. Preliminary concepts for further development of the production and control of these inactivated virus vaccines are discussed.