Eicosatrienoic Acid (20:3ω-3) is a rare PUFA of the ω-3 series. In normal humans, it represents less than 0.25% of serum phospholipid fatty acids. However, it is one of the most active essential fatty acids when assayed for the inhibition of fatty acid elongation/desaturation reactions which convert dietary C-18 fatty acids to C-20 eicosanoid precursors.