We examined time related effects of an intake of n-3 polyunsaturated fatty acids (PUFA) on the fatty acid profiles of rat enterocyte phospholipids. Three diets containing 20 wt% fat with similar levels of linoleic acid (C18:2n-6), approximately 11 wt% of the fatty acids, were prepared. The diets were: Palm oil diet (PD), 0.6 wt% n-3 PUFA; fish oil diet (FD), 32 wt% n-3 PUFA (C20-C22); and linseed oil diet (LD), 32 wt% n-3 PUFA (C18:3n-3). Forty weanling male Wistar rats were fed PD for 34 days and then divided into three groups. Two groups of sixteen rats each were then fed FD or LD, respectively, and eight rats remained on PD as a control group. At 6, 12, 18, 24, 72, 144, and 288 hours following the change of diets rats were killed, the enterocytes were isolated and the fatty acid profiles of the intestinal phospholipids were examined. During the first 12 hours following the change from PD to FD, the content of n-3 PUFA in the intestinal phospholipids increased from less than 1 mol% to approximately 20 mol%, whereas the contents of n-6 PUFA and of monoenes were reduced from 40 mol% to 28 mol% and from 19 mol% to 12 mol%, respectively. The fatty acid profiles were then largely constant during the remaining experimental period. In the LD group, the n-3 PUFA contents rose from less than 1 mol% to 10 mol% during the first 144 hours, and the content of n-6 PUFA and monounsaturated fatty acids were reduced from 40 mol% to 36 mol% and from 19 mol% to 14 mol%, respectively. Desaturation and elongation products of C18:3n-3, such as C20:5n-3, C22:5n-3 and C22:6n-3, were observed following intake of LD. All three groups contained approximately 40 mol% of saturated fatty acids in the intestinal phospholipids. Copyright (C) 1996 Elsevier Science Inc.