The requirements for essential fatty acids in patients on home parenteral nutrition are not well described. We therefore studied the needs of 12 patients receiving parenteral nutrition for at least 4 mo (range: 4 mo-17.3 yr; mean 7.0 +/- 5.2 yr). Prior to the study, each patient had been receiving intravenous lipids either weekly or biweekly and had a triene to tetraene ratio (TTR) on plasma phospholipids performed at least annually. A TTR > or = 0.2 was considered diagnostic for essential fatty acid deficiency (EFAD). The purpose of this study was to determine the required intravenous lipid supplementation in patients on home total parenteral nutrition (HTPN). Patients with an initial TTR of < 0.2 had their intravenous lipid stopped and changes in their serum phospholipid fatty acids were followed every 3-4 wk. Nine of 12 patients had TTRs > 0.2 at some point in the study. Phase I consisted of patients who at initiation of the study had normal TTRs and were taken off lipid supplementation until their TTR became abnormal. Phases II, III, IV, and V consisted of lipid delivered in total nutrient admixtures in biweekly doses of 0.6, 1.2, 1.8, and 2.4 g of fat/kg bodyweight, respectively. Eight patients normalized their TTRs on the biweekly lipid regimens; one patient expired before his ratio normalized; and three patients could not be made deficient in essential fatty acids after 26 or more wk of fat-free parenteral nutrition. Most patients required 1.2 to 2.4 g of lipid/kg bodyweight/biweekly to correct serologic EFAD. The clinical background, as well as the length of small bowel remaining, did not seem to identify those patients who required lipid supplementation nor the final dose of lipid needed to normalize their TTRs.