Adipose-tissue fatty acid composition was studied in nine patients requiring long-term total parenteral nutrition (TPN). The patients received 17 +/- 8% of total energy as soybean-oil emulsion (Intralipid) and 66 +/- 8% as glucose. Despite low intake of 9c-16:1, 11c-18:1, and 13c-18:1, adipose-tissue concentrations of these monounsaturated fatty acids were higher in the TPN patients than in free-living control subjects (P less than 0.05) and inversely correlated with the percent energy from fat (r = -0.56, P = 0.11; r = -0.64, P = 0.06; r = -0.81, P = 0.008, respectively). This suggests that these fatty acids accumulated from endogenous synthesis from carbohydrate and thus may be markers of the percent fat in the diet. The essential fatty acids, 18:2 and 18:3n-3, positively correlated with the percent energy from fat (r = 0.79, P = 0.01; r = 0.80, P = 0.01, respectively). Linear-regression analysis suggests that normal adipose-tissue stores of 18:2 and 18:3n-3 are maintained when intravenous soybean-oil emulsion provides 11-20% and 4-12%, respectively, of total energy.