The effect of supplementation with the omega 3 polyunsaturated fatty acid (n3 PUFA) docosahexaenoic acid (DHA) on membrane composition and amyloid-β₁₋₄₂ (Aβ₄₂) secretion was studied in human amyloid-β protein precursor-transfected Chinese Hamster Ovary (CHO) cells. Twenty-four hour incubation with a range of DHA concentrations resulted in a dose-dependent increase in membrane DHA and eicosapentaenoic acid content and a decrease in arachidonic acid content. In addition, DHA supplementation caused a dose-dependent reduction in the secreted Aβ₄₂ levels and resulted in a 4-8 fold decrease in extracellular prostaglandin E₂ (PGE₂) levels. Tocopherol, which was added to DHA to prevent oxidation, may have contributed to the effect of DHA, since it slightly decreased extracellular Aβ₄₂ and PGE₂ levels when given alone. The addition of selective COX2 inhibitors Celebrex and curcumin to the culture medium resulted in a significant and comparable inhibition of PGE₂ release, but did not inhibit Aβ₄₂ secretion, and even significantly increased Aβ₄₂ production in this cell system. Together, the present data show that, whereas both DHA and COX2 inhibitors may reduce PGE₂ production, only DHA in the presence of tocopherol significantly reduced Aβ₄₂ production and concurrently changed membrane lipid composition in CHO cells. It is concluded that in this in vitro setting DHA reduced Aβ₄₂ secretion through membrane-related, but not PGE₂-related mechanisms.