Recombinant bovine interleukin‐2 was evaluated as a potential immunoenhancer of bovine mammary gland mononuclear cells. Bovine mononuclear cells were isolated from five primiparous Holstein cows at 14–18 and 28–32 days of involution and at 7–13 days prior to parturition. Optimal stimulatory concentrations of the T‐lymphocyte mitogen concanavalin A and the T‐dependent B‐lymphocyte mitogen pokeweed mitogen were determined to be 6.25 and 2 μg ml‐1respectively. Proliferation of mononuclear cells in response to recombinant bovine interleukin‐2 was evaluated in the presence of suboptimal concentrations of concanavalin A and pokeweed mitogen to avoid masking potential effects of recombinant IL‐2. Bovine blood and mammary gland mononuclear cells were highly responsive to mitogens and to recombinant bovine interleukin‐2. The response of mammary gland mononuclear cells to recombinant bovine interleukin‐2 was comparable with the response of blood mononuclear cells. The data suggest that recombinant bovine interleukin‐2 may be an effective in vivo immunoenhancer of mammary gland mononuclear cells.