Sulfur mustard (HD) is a potent vesicating agent of military importance, with known radiomimetic properties. The euthymic hairless guinea pig (EHGP) (Cavia porcellus) is emerging as the animal model of choice for cutaneous HD study. With elucidation of the systemic effects, we may better utilize this animal for all HD toxicity work. To this end, studies were conducted to determine the definitive median lethal dose (MLD) of subcutaneously applied sulfur mustard (HD) in the EHGP, and to correlate the induced hematological changes. Eight groups of two animals each were dosed at 0.3 log intervals from an extrapolated expected dose, deriving a tentative mean around which five groups of six animals each were dosed at 0.1 log intervals, resulting in a definitive MLD of 48.17 mg kg(-1). Sulfur mustard was then administered to seven groups of six animals each at a dose of 30 mg kg(-1) and hematology performed. Significant leukocyte count suppression was found to occur on days 4, 5 and 6, following a leukocyte elevation on day 1 after exposure. Serum potassium levels were found to be elevated all 7 days after HD exposure. Establishing the MLD for subcutaneously applied HD and the pattern of induced leukocyte suppression allows for more definitive evaluation of successful toxicity counter-measures.