This research is an investigation of the utilization of essential fatty acids by normal human skin fibroblasts. It seeks to investigate homeostatic mechanisms for maintaining phospholipid fatty acid composition, including regulation of fatty acid desaturation by exogenous polyunsaturated fatty acids, and selective utilization of specific fatty acids in membrane phospholipids while others are stored in triglyceride droplets. Changes in phospholipid acyl composition affect membrane adhesiveness and fluidity as well as availability of prostaglandin precursors. With proposed modification of the American diet to increase consumption of polyunsaturated fatty acids as a component in the prevention of atherosclerosis, it is important to understand how normal human cells respond to these nutritional modifications.