.DELTA.2-cis Eicosenoic acid is an α,β-unsaturated fatty acid that has been extracted from fresh water clams and purified. A related compound, 2-octadecenoic acid, has been shown to improve liver function and decrease blood sugar in streptozocin-induced diabetic rats. .DELTA.2-cis Eicosenoic acid and its salts have potential medicinal use for treating diabetes and improving lipid metabolism.