Docosahexaenoic acid (DHA, 22:6Δ4,7,10,13,16,19) is the longest chain and most unsaturated fatty acid commonly found in biological systems . It represents the extreme example of the important class of fatty acids known as omega-3s. Primarily through dietary studies, this fatty acid has been linked to an enormous variety of human afflictions including cancer [2, 3], heart disease , rheumatoid arthritis , lupus , alcoholism , blindness , respiratory diseases , peroxisomal disorders , cystic fibrosis , schizophrenia , depression , malaria , multiple sclerosis  and even migrane headaches. In order for one simple molecule to affect so many seemingly unrelated processes it must function at a fundamental level, common to most cells. It has been suggested that this level is in controlling membrane structure and function . Due to its extreme chain length and unsaturation it should be easier to demonstrate a unique role for DHA in membrane structure/function than it will be for other shorter, less unsaturated fatty acids commonly found in membranes. Reviewed here is the possible involvement of DHA in membrane lipid domains.