Histones induce transient anemia and enhance splenic uptake of erythrocytes. Five groups of BALB/c mice were injected IV with 50 mg/kg of histones or PBS, and 1 group was euthanized at each 5, 10, 20, and 30 minutes postinjection for determination of (A) the number of circulating erythrocytes, (B) plasma hemoglobin (Hb) concentration, (C) Hb uptake by the spleen, (D) circulating leukocyte numbers, and (E) circulating platelet numbers. In this experiment, 5-week-old mice were used, but very similar results were obtained with 8-week-old animals (data not shown). Results are representative of 3 separate experiments. Data are expressed as the mean ± standard error of the mean (n = 5). **P < .01; ***P < .001; ****P < .0001 (1-way analysis of variance with Tukey’s multiple comparisons test). NS, not significant.