Abstract: Methods and reagent kits for the detection of intracellular antigens such as TdT and antinuclear antibodies. The methods involve swelling the cells with a hypotonic solution for increasing the localization of large molecular weight substances such as antibodies at intracellular antigenic sites, fixing the cells and reacting them with antibodies specific for the intracellular antigen to be detected. The cells are then further reacted with labeled antibody specific for the first antibody, washed to remove unreacted antibodies and the presence of label detected whereby the presence or absence of the intracellular antigen may be determined.