The original Westergren blood sedimentation technique was modified to assess leukocyte sedimentation properties. The relative change of leukocyte and erythrocyte counts was measured in the upper half section of blood column in vertically positioned sedimentation tubes in 10-minute-intervals for 60 minutes. During the first 20 minutes of gravity sedimentation, the leukocytes taken from critically ill patients showed upward flotation, however, healthy individuals' leukocytes demonstrated slight sedimentation. The upward flotation rate of leukocytes seemed less dependent on erythrocyte sedimentation during the first 15 minutes of sedimentation time than after it. Based on this observation, the sedimentation properties of leukocytes were characterized by the leukocyte antisedimentation rate taken at the 15th minute of sedimentation time (LAR15). Erythrocyte aggregability index, plasma fibrinogen concentration and native leukocyte count did not correlate to LAR15 in healthy volunteers (n = 25). However, LAR15 was correlated to leukocyte adherence (p < 0.01), to whole blood viscosity (p < 0.05), to hematocrit (p < 0.05) and to the conventional erythrocyte sedimentation rate (p < 0.05).