Lymphocytes from human palatine tonsils were cultured in vitro with either Sabin poliovirus-2 or polyvalent Salk vaccine. Specific antibody was demonstrated in culture fluids after 7 days incubation. The specific antibody was found to be of the IgM class as determined by selective adsorption with monospecific antiserum to human IgM and by an indirect blocking fluorescent antibody technique. The production of this specific antibody was dependent on DNA synthesis 3 days before the detection of specific antibody. Suppression of specific IGM antibody production was caused by actinomycin-D or mitomycin-C when added simultaneously with antigen. However, when the inhibitors were added 72 hr after antigen treatment, only the actinomycin-D was effective in suppressing specific antibody production.