Titers of antibody to poliovirus in 102 patients were determined with a sensitive neutralization assay before and 1 year after autologous bone marrow transplantation. At 1 year 14 patients (14%) had lost antibodies to poliovirus type 1 (P < .001), 10 (10%) to poliovirus type 2 (P < .05), and 13 (13%) to poliovirus type 3 (P < .01). Twenty-two patients had lost antibodies to at least one type of poliovirus. Follow-up of unimmunized patients 2 years (n = 40) and 3 years (n = 23) after transplantation documented a continuous decrease in antibody titer; by 3 years after transplantation, another 6 patients had become seronegative. When one dose of inactivated trivalent poliovirus vaccine was administered 1 year after transplantation, 2 (25%) of 8 patients seronegative for poliovirus type 1 had an increase of at least fourfold in antibody titer; after three doses, 10 (83%) of 12 patients exhibited such an increase (P < .05). The corresponding figures were 5 (71%) of 7 and 13 (100%) of 13 for poliovirus type 2 (difference not significantly) and 2 (22%) of 9 and 14 (88%) of 16 for poliovirus type 3 (P < .01). These results indicate that at least 30% of patients undergoing autologous bone marrow transplantation including those seronegative for poliovirus before transplantation will benefit from reimmunization with three doses of inactivated trivalent poliovirus vaccine 1 year after transplantation.