Poliovirus capsid proteins (VP's) were isolated by DEAE-Sepharose chromatography in the presence of RNA-se and 9 M urea or by preparative SDS-polyacrylamide gelelectrophoresis (SDS-PAGE). With the first method, several, but not all, capsid proteins, from the three different virus types could be isolated in pure form, probably because of incomplete dissociation of the virus particles in 9 M urea. With SDS-PAGE all capsid proteins could be isolated in pure form. Immunization of rats and rabbits with the three largest VP's (VP1, VP2 and VP3) isolated by both methods, resulted in the induction of neutralizing antibodies already after 2-3 injections, provided the capsid proteins were isolated from formalin inactivated virus. Apparently formalin treatment stabilized the antigenic determinants, which are responsible for induction of neutralizing antibodies, against denaturation upon VP-isolation. In contrast to several other picornaviruses, where only one of the VP's induces neutralizing antibodies, for poliovirus both VP1, VP2 and VP3 are able to induce neutralizing antibodies. VP's isolated from live virus did not induce neutralizing antibodies, but were able to "prime" the animals. Primary vaccination with any of the VP's, followed by a second injection with a low dose of vaccine (D-antigen) resulted in a boosterlike production of neutralizing antibodies against the D-antigen, even D-antigen of a heterotypic virus. This indicates the occurrence of common antigenic regions on the different capsid polypeptides.(ABSTRACT TRUNCATED AT 250 WORDS)