Advances in the understanding of neutrophil biochemistry require the development of effective procedures for isolating purified neutrophil populations. Although methods for human neutrophil isolation are now standard, similar procedures for isolating neutrophils from many of the nonhuman species used to model human diseases are not as well developed. Because neutrophils are reactive cells, the method of isolation is extremely important to avoid isolation technique-induced alterations in cell function. We present methods here for reproducibly isolating highly-purified neutrophils from large (cow, horse, sheep) and small (mouse, rabbit) animal models and describe optimized details for obtaining the highest cell purity, yield, and viability. We also describe methods to verify phagocytic capacity in the purified cell populations using a flow cytometry-based phagocytosis assay.