Digestibilities of cis and trans docosenoic acids (C 22:11) have been determined in male growing Wistar rats. Eight groups of rats were fed diets with 0.04 or 0.92% calcium and 15% lipids; the latter contained about 46% cis or trans C:22:1, and 1.5 or 28% linoleic acid. Food consumption was recorded and faeces were collected during 9 days. Fecal lipids were extracted in two fractions: soluble (in chloroform), and insoluble; the fatty acids of both fractions were analysed by gas-liquid chromatography. Calcium and, in some cases, Phosphorus, were determined in the soluble fraction. The digestibility of brassidic acid was strongly lowered by the presence of Calcium in the diet (-35 points). This was due to the massive formation, in the gut, of insoluble Calcium complexes (probably Calcium soaps) of brassidic acid. Dietary linoleic acid improves the absorption of brassidic acid (+ 17 points). This effect could result from the lower melting point of the dietary fat (37 degrees C instead of 48 degrees C) and/or from the emulsifying properties of monolinolein in the intestine. The effects of Calcium and of linoleic acid were additives. In the most favourable conditions (no Calcium, 28% linoleic acid), brassidic acid digestibility reached 98%. Erucic acid digestibility was decreased by dietary Calcium, but to a lesser extent than that of brassidic acid (-17 points). Here again, the formation in the gut of Calcium erucate and Calcium-Phosphorus-erucate complexes was responsible of this phenomenon. As a matter of fact, the digestibility of erucic acid reached nearly 100% when no Calcium was added to the diet. The absorption of erucic acid was not improved by dietary linoleic acid.