Leukocyte differential analysis was performed in various species, particularly laboratory animals, by the laser multi-angle polarized light scattering separation method. Venous blood specimens were drawn from the following subjects: healthy adult men and women ("humans"); cynomolgus monkeys ("monkeys"); common marmosets ("marmosets"); beagle dogs ("dogs"); miniature potbelly pigs ("swine"); Japanese white rabbits ("rabbits"); Hartley guinea pigs ("guinea pigs"); and Sprague-Dawley rats ("rats"). 90°/10° scatter plot: Basophils and mononuclear-polymorphonuclear cells were separated in all subjects, but individual 10° and 90° scatter plots overlapped in dogs and guinea pigs, respectively. 90° depolarized /90° scatter plot: Neutrophils and eosinophils were clearly separated in human, monkey, guinea pig, swine and rat subjects. The eosinophil cluster was not clearly plotted in marmoset, dog, or rabbit. 0°/10° scatter plot: Regarding this plot for monocytes and lymphocytes, cells were plotted in the following order in all subjects: lymphocytes < basophils ≤ monocytes in the 0° (size) scatter; and lymphocytes approximatery equal to monocytes ≤ basophils in the 10° (complexity) scatter. Compared to other species, the rat scatter showed a tendency to overlapping plots in both the 0° and 10° scatters in the monocyte and lymphocyte clusters. In both dog and guinea pig, the monocyte and neutrophil plots overlapped in the 0° and 10° scatters. Basobox: In the human and rabbit subjects, the basophil cluster was plotted within the established basobox, but no clear cell cluster was plotted in the other subjects. As a result of comparing the percentage values for leukocytes in various species obtained by using the CD3500 apparatus versus the corresponding values obtained manually, good correspondence was found in the monkey, and eosinophils in the marmoset were lower with CD3500 than manually. In the rabbit, the mean measured value for basophils matched in the manual and CD3500 findings. In the guinea pig, the CD3500 values were lower than the manual values for lymphocytes, but higher for monocytes and neutrophils. The above findings suggest that the laser multi-angle polarized light scattering separation method is indeed capable of analyzing leukocytes from various species based on cell size and cell complexity, i.e., the presence or absence of nuclei, granules and cell enclosures.