Abstract Interleukin 2 (IL-2), secreted by bovine peripheral blood mononuclear cells (PBL) on stimulation with concanavalin A (Con A), was purified and characterized by different chromatographic and electrophoretic techniques. The ability of IL-2 to support proliferation of Con A-stimulated bovine lymphoblasts was used to assay and quantitate IL-2 activity. Bovine IL-2 having an apparent MW of 27 000 eluted from a gel-filtration column; from an anion exchange column peak activity was detected at 190 m M NaCl. Binding of bovine IL-2 to phenyl-Sepharose gel and elution with 35–60% ethanediol indicated its hydrophobic nature. Studies on cross-species reactivity revealed that both buffalo and goat lymphocytes respond to cattle IL-2 and detected 35% of activity from a standard cattle IL-2 preparation. Sheep lymphocyte response to cattle IL-2 was negligible.