Summary: The production of specific antisera against two type-specific antigens of poliomyelitis, N and H, in guinea pigs is described. Heated poliomyelitis virus preparations when injected intraperitoneally into these animals induced antibodies that reacted solely with heated (H) homologous antigen, but not with fully infectious native (N) antigen. These sera were devoid of neutralizing antibodies. For preparation of anti-N sera, recourse had to be taken to serum absorption techniques. Immunization of guinea pigs with fully infectious virus preparations stimulated antibodies against both N and H antigens in the great majority of animals tested. Anti-H could be absorbed with H-antigen, leaving sera that reacted solely with N-antigen of a single type of virus.