A high level of atmospheric particulate matter induces an increase in circulating polymorphonuclear leukocyte (PMN) counts and an increase in serum inflammatory cytokine levels. The particulate level in Antarctica is extremely low compared with that in industrial countries. We hypothesized that this low level would reduce circulating leukocyte counts and serum inflammatory cytokine levels in people visiting Antarctica from industrial countries. The number density of particulates with aerodynamic diameters of <10.0 microm was measured in Japan and in Antarctica during the 41st Japanese Antarctic Research Expedition. Circulating leukocyte counts, granulocyte colony-stimulating factor and interleukin-6 levels, and pulmonary function were determined at regular intervals in 39 expedition members. The particulate number density was <1% of that measured in Japan. Total leukocytes, segmented and band-formed PMN, monocyte counts, and serum interleukin-6 levels decreased in Antarctica compared with the initial values measured in Japan. Pulmonary function parameters did not change except for maximal voluntary ventilation. Particulate matter levels had more significant effects on segmented PMN, band-formed PMN, and monocyte counts than cigarette smoking and the type of work. Exposure to reduced atmospheric particulates is considered to be a major factor for decreasing circulating leukocyte counts and serum cytokine levels.