Arm II (isotope study): Patients meeting the same criteria as in arm I receive oral D5-labeled linolenic acid and oral D4-labeled linolenic acid that is dissolved in oil and incorporated into foods. Subjects must avoid eating fish and shellfish during the 35 days of the isotope study. Blood samples are collected at 0, 8, 24, and 48 hours, daily on days 3-7, and then on days 10, 18, and 35.