Abstract Arachidonic acid (AA) metabolites and reactive oxygen species (ROS) are implicated in the suppression of interleukin-2 (IL-2) activity. We investigated the effects of aci-reductones, compounds that function both as inhibitors of AA metabolism and as scavengers of ROS, on the generation of IL-2-induced, lymphokine activated killer (LAK) activity. Aci-reductones belonging to the 4-aryl-2-hydroxytetronic acid system improved the in vitro generation of LAK activity from IL-2-treated human peripheral blood mononuclear cells (PBMC) approximately 4-fold. Those aci-reductones belonging to the 3,4-dihydroxyhenzofuranone class were less effective. LAK activity improvement was comparable to that produced by indomethacin with superoxide dismutase plus catalase and comparable to the improvement produced by depleting PBMC of monocytes. Aci-reductones completely suppressed the production of prostaglandin E 2 from PBMC in response to IL-2 and partially suppressed superoxide anion production. Daudi cell and lymphocyte subset proliferation and monocyte viability were not affected. Less improvement in LAK activation was observed when PBMC depleted of monocytes were exposed to IL-2 and aci-reductones. We conclude that aci-reductones improve LAK generation from PBMC in vitro. This property may be mediated via effects on monocyte AA and ROS metabolism.