[en] The delayed-type hypersensitivity (DTH) reaction observed in mice primed i.v. with low doses of sheep red blood cells was greatly decreased when mice were irradiated with 300 rad before priming. An estimation of the radiosensitivity of DTH-mediating cells (DTH-C) was performed using a titration assay after local adoptive transfer of these cells mixed with antigen into the footpad of unprimed mice. A high radiosensitivity of the induction of DTH-C was observed with a D37 of approximately 50 rad. In contrast, the expression of DTH-C appeared radioresistant, as the D37 was approximately 2000 rad. (author)