IT is important that a virus reference laboratory be able to hold viruses in the infectious state for long periods and to transmit them long distances. We have experienced difficulty with some newly isolated viruses of the respiratory tract. Some preparations of para-influenza viruses and rhinoviruses have become non-infectious after being frozen at below −;60° C in the presence of 2 per cent bovine plasma albumen or 2 per cent calf serum respectively for a year or more; the former viruses rapidly become non-infectious at room temperature1 and so have been transported in the frozen state or as infected tissue cultures. In earlier experiments virus was preserved by freeze-drying, but much infectivity was lost. In recent experiments viruses seem to have been better stabilized, and the results are reported here.