The present study was designed to explore the range of biologic activity of an anti-lymphokine antiserum (ALKS). This preparation, which was produced by a two-stage immunization procedure, was used to prepare Sepharose bead immunoadsorbent columns. Columns made with ALKS, but not with anti-control antiserum, could specifically remove MIF activity, but not LT, MF, or NCF activity from activated lymphocyte culture supernatants. MIF, but not LT, MF, or NCF could be recovered from the beads by acid extraction. These findings, taken in conjunction with the previously described capacity of ALKS to remove MCF and SRF activity from supernatants, demonstrate that ALKS, although prepared against a lymphokine preparation with multiple activities, has restricted specificity. Thus far, its targets appear to be those mediators that affect macrophages either in vitro or in vivo. The capacity of ALKS to suppress delayed hypersensitivity reactions in the guinea pig is consistent with these observations, since the macrophage is the predominant infiltrating cell in those reactions.