The antigenic preparations have been kept at, --20 ° C for 11 months without loss in reactivity, Itaemagglutinating (HA) antigens can be produced ~om infected SMB by the SA extraction method of CL~R~:E and CASALS (4), hut Mso suspensions of crude infected SMB and PEG 6000/NaC1 precipitated cell culture fluids contain haemagglutinating activity.