At least 3 complement factors were found necessary for the conversion of the thermolabile intermediate complex EAC'1a,4,2a to a thermostable state. One of these factors is the earlier described beta(1C)-globulin. The second, a heretofore unrecorded serum protein, beta(1F)-globulin. The third factor has not yet been defined as a discrete serum protein entity. Kinetic experiments indicated that b...