Deterioration of food quality via oxidative rancidity is often the primary factor limiting the shelf life of food products, even in foods that have low fat content. For many food products, the membrane constituents of the cells comprising the food are the primary sites of peroxidative damage. This is probably related to the surface exposure of membrane phospholipid molecules to the aqueous phase containing peroxidation-initiating species. The extent to which oxidation of fatty acids and their esters occurs in foods depends on the chemical structure of the fatty acid, the nature of food processing, the temperature at which the foods are stored and/or cooked, and the minor constituent antioxidants. Incorporation of antioxidants into food products may impart signiﬁcant health beneﬁts to consumers in addition to stabilizing the food product. The need to screen large numbers of compounds for antioxidant activity requires rapid and sensitive assays for evaluating the free radical scavenging, membrane protective activities. This report described in vitro screening experiments of two Apiaceae medicinal plants to address this need.