In order to explain why the DNA concentration and the number of cells increase in adipose tissues with the proportion of linoleic acid given to rats, some determinations were carried out either on epididymal fat pads, or on isolated adipocytes (in a whole), or on their cellular fractions (ghosts, nuclei, mitochondria microsomes). Weaning rats were fed a 20% fat diet containing either lard (S) or sunflower oil (T). After 82 days of dietary treatment, animals were sacrificed after a 16-hour fast. Water and lipids were more abundant in whole epididymal S tissues than in T tissues and in isolated adipocytes: Lipid/DNA and RNA/DNA ratios were also higher in S than in T. These values were: 30.10-3 and 20.10-3, 3.98 and 2.49 for S and T, respectively. Differences in protein concentrations were not especially visible neither in the cytosol fraction nor in nuclei and microsomes. However, mitochondria were disturbed by the lipid composition of dietary fats and the concentration of proteins was twice less elevated in S than in T. Fatty acid composition was determined on cellular fractions after 3 weeks (adipocytes) or 3 months of dietary treatment (ghosts). No difference in phospholipid concentration of arachidonic acid was found in all cellular fractions (nuclei, mitochondria, microsomes) while large differences were observed in the concentration of oleic acid (more elevated in S) and in the concentration of linoleic acid (more elevated in T). All these differences, which actually indicate important structural alterations, could be at the origin of the adipose tissue versatile behaviour, according to the fatty acid composition of exogenous fats – and namely – to the linoleic acid proportion included in the diet