Epidemiological data indicate that omega-3 fatty acids protect from cardiovascular diseases and hyperlipidemia. Cold water fish is the major recognized source of omega-3 fatty acids but fish is not a staple food in many countries. Since terrestrial green plants may also represent a source of omega-3 fatty acids we tested the hypothesis that platelet rich plasma and milk from cows feeding exclusively on green grass contains more omega-3 fatty acids than milk from cows fed conserved grass. The relative concentrations of linolenic acid (18:3) and eicosapentaenoic acid (20:5) and the ratio of eicosapentaenoic acid to arachidonic acid (20:4) which is critical for the formation of omega-3 derived eicosanoids were significantly higher in milk from grass fed cows. Similar changes were seen in the fatty acid composition of platelets. Half a liter of milk from grass-fed cows provides approximately 191 mg 18:3 and 14 mg 20:5. In this regard milk from grass fed cows may be nutritionally superior to milk from cows eating conserved grass.