The electrophoretic migration of the antigens of six poliovirus strains was studied by immunoelectrophoresis in agarose gel at pH 8.2 and pH 7.0. Differences in migration were observed: the H antigens migrated faster than the corresponding N antigens. A small variation in migration between different poliovirus types was observed; also intratypic variation was noted (most pronounced between poliovirus type 1 strains Brunhilde and Chat). All antigens were negatively charged at pH 8.2 and 7.0, except the Brunhilde N antigen at pH 7.0. This antigen had a slight positive charge at this pH, suggesting an isoelectric point just above 7.0 under the conditions tested.