The influence of recombinant bovine interleukin‐2 (rBoIL‐2) on mammary gland mononuclear cell proliferation in the presence of lactoferrin and serum albumin was evaluated. Mammary mononuclear cells were isolated from five pregnant Holstein cows during the periparturient period and cultured with 0, 2.5 or 25 ng ml‐1of rBoIL‐2. Lactoferrin and serum albumin were evaluated at concentrations ranging from 0 to 2.5 mg ml‐1. Both 2.5 and 25 ng ml‐1of rBoIL‐2 significantly increased mononuclear cell proliferation. Increasing concentrations of lactoferrin resulted in a dose‐dependent reduction of mononuclear cell proliferation in the presence and absence of rBoIL‐2. However, in cells from four of the five cows, rBoIL‐2 treatment (2.5 and 25 ng ml‐1) resulted in significantly enhanced mononuclear cell proliferation compared to controls (no rBoIL‐2) even in the presence of the highest concentration of lactoferrin. Serum albumin had little influence on mononuclear cell proliferation. Results of this study suggest that lactoferrin inhibits mammary gland mononuclear cell proliferation, and that rBoIL‐2 can overcome lactoferrin‐induced hyporesponsiveness.