Electrophile-mediated disruption of cell signal-ing is involved in the pathogenesis of several diseases including atherosclerosis and cancer. Diffusible and membrane bound lipid electrophiles are known to modify DNA and protein substrates and modulate cellular pathways including ER stress, antioxidant response, DNA damage, heat shock, and apoptosis. Herein we report on a structure-activity relationship for several electrophilic analogues of 4-hydroxynonenal (HNE) and 4-oxononenal (ONE) with regard to toxicity and anti-inflammatory activity. The analogues studied were the oxidation products of HNE and ONE, HNEA/ONEA, the in vivo hydrolysis products of oxidized phosphatidylcholine, COOH-HNE/COOH-ONE, and their methyl esters, COOMe-HNE/ONE. The reactivity of each compound toward N-acetylcysteine was determined and compared to the toxicity toward a human colorectal carcinoma cell line (RKO) and a human monocytic leukemia cell line (THP-1). Further analysis was performed in differentiated THP-1 macrophages to assess changes in macrophage activation and pro-inflammatory signaling in response to each lipid electrophile. HNE/ONE analogues inhibited THP-1 macrophage production of the pro-inflammatory cytokines, IL-6, IL-1β, and TNFα, after lipopolysaccharide (LPS)/IFNγ activation. Inhibition of cytokine production was observed at submicromolar concentrations of several analogues with as little as 30 min of exposure. Phagocytosis of fluorescent beads was also inhibited by lipid electrophile treatment. Lipid electrophiles related to HNE/ONE are both toxic and anti-inflammatory, but the anti-inflammatory effects in human macrophages are observed at nontoxic concentrations. Neither toxicity nor anti-inflammatory activity are strongly correlated to the reactivity of the model nucleophile, N-acetylcysteine.