Adipocytes secrete bioactive molecules called adipokines which exert both local and systemic effects. Resistin, a novel cysteine-rich secretory protein, was originally identified as a murine adipokine, and proposed to link obesity, insulin resistance and cardiovascular disease. However, the (patho)physiological role of human resistin, which exhibits significant sequence divergence from its murine counterpart, and is secreted predominantly from macrophages, rather than adpiocytes, remains controversial. Here, we hypothesized that resistin may regulate macrophage cholesterol homeostasis, and lipid accumulation, possibly via regulation of 5’-AMP activated protein kinase (AMPK). The effect of human recombinant resistin on lipid metabolism was studied using human THP-1 macrophages, which do not express or secrete endogenous resistin. Treatment (24h) with resistin (0-100 ng ml-1) significantly increased cholesteryl ester mass by up to 172% and 229%, in the absence or presence of oxidized LDL (50 μg ml-1), respectively, and increased incorporation of [3H]cholesterol (140.1%) and [3H]oleate (163.4%) into the cholesteryl ester pool, compared with control untreated cells. Incorporation of [3H]oleate into the cholesteryl ester pool was blocked by an ACAT inhibitor (10 μM Sandoz 58-035; p<0.01); however, expression of ACAT-1 mRNA or protein were not affected by treatment with resistin. The observed increases in the cholesteryl ester pool could not be explained by changes in macrophage cholesterol efflux mechanisms, as resistin did not impact upon apoAI/apoE dependent cholesterol efflux, or expression of ABCA1. Resistin did, however, significantly increase triacylglycerol accumulation in THP-1 macrophages, by 148% of untreated control cells (p<0.01). Intriguingly, the ‘anti-obesity’ agent, C75, which inhibits fatty acid synthesis and promotes fatty acid oxidation, effectively inhibited resistin-induced cholesteryl ester and triacylglycerol mass accumulation, suggesting that altered fatty acid metabolism might explain these increases in macrophage neutral lipid mass. Uptake of [3H]oleate was significantly increased (119% of control; p<0.05) by preincubation with resistin (50 ng ml-1), while oxidation of [14C]oleate was reduced by nearly 30% after exposure to resistin (p<0.05). These effects were accompanied by a significant reduction in AMPK activity, as judged by phosphorylation of acetyl CoA carboxylase (ACC). Thus, treatment with resistin causes alterations in macrophage fatty acid metabolism, contributing to triglyceride and cholesteryl ester deposition, which may predispose ‘foam cell’ formation and atheroma progression.