The effect of leukopenia on the susceptibility of rabbits to the localized Shwartzman reaction was studied in those receiving whole body irradiation and nitrogen mustard respectively. Of animals receiving nitrogen mustard in which the total polymorphonuclear leukocyte count was less than 100 cells/c.mm. only 17 per cent developed positive local Shwartzman reactions whereas 75 per cent of irradiated animals with total polymorphonuclear leukocyte counts less than 100 cells/c.mm. had positive reactions. A local Shwartzman reaction occurred in 60 of 71 control rabbits (85 per cent). Animals of both the treated groups showed positive Shwartzman reactions at a time when their total polymorphonuclear leukocyte counts were less than 500 cells/c.mm.
From the findings, it is concluded (a) that the presence of normal numbers of circulating polymorphonuclear leukocytes is not an obligatory prerequisite condition to the localized hemorrhagic necrosis of the Shwartzman phenomenon, and (b) the mechanisms of action of nitrogen mustard and whole body irradiation on body tissues differ in relation to the Shwartzman reaction.