RECENT work with adenovirus1, Sindbis virus2 and the viruses causing influenza3, measles4, vesicular stomatitis5 and German measles6 has shown that subunits of the viruses can stimulate the production of neutralizing antibodies, and in some cases can be used as vaccines. Subunits are usually present in unfractionated virus preparations and in the case of the lipid-containing viruses can also be produced from complete virus particles by treating with ‘Tween’-ether or a detergent, for example, sodium deoxycholate or sodium dodecyl sulphate. The use of subunits for immunization has the important advantage that it avoids the side effects from other components of the virus. We report here preliminary experiments with rabies virus in which subunits separated from virus suspensions were shown to be potentially useful for protection against the disease.