Abstract The fatty acid patterns of triglycerides and phospholipids extracted from adipose tissue, liver, heart, kidney, spleen, and lung of 3 groups of C57BL/6 mice were determined after feeding diets rich in palmitic acid (16:0) (high palmitic: 16:0 = 45.1% of total fatty acids), stearic acid (18:0) (high stearic: 18:0 = 42.9% of total fatty acids) and oleic acid (18:1) (high oleic: 18:1 = 79.7% of total fatty acids) for 9 months. Triglyceride content of adipose, liver, heart, kidney, lung and spleen tissues was significantly enriched in palmitic acid in mice fed the high palmitic diet (range among all tissues: 19.9% ± 0.2% to 29.0% ± 1.9% of total fatty acids) and in oleic acid in mice fed the high oleic diet (range 56.0% ± 1.9% to 71.6% ± 1.2%). The stearic acid content of organ triglycerides in mice fed the high stearic diet ranged from 3.7% ± 0.3% to 10.8% ± 1.2%; however, the content of oleic acid on this diet (range; 57.0% ± 1.8% to 71.4% ± 1.7%) was similar to the one observed in mice fed the high oleic diet. In all organs, phospholipids had a significantly higher percentage of stearic acid (range: 23.5% ± 0.9% to 51.5% ± 6.6%) than triglycerides, regardless of diet. To evaluate the production of oleate from stearate and palmitate, 2 groups of mice were fed the high palmitic and the high stearic diets for 1 week and then injected intravenously with [1- 14C]palmitate and [1- 14C]stearate and the amount of labelled oleate in liver triglycerides was measured. In liver triglycerides of mice injected with [1- 14C]stearic acid, more than 80% of 14C label recovered was bound to oleic acid, while in mice injected with radioactive palmitate, the maximum recovery of label bound to oleate was 47.0% ± 6.9%. These data suggest that stearic acid is rapidly converted into oleic acid and could help explain why dietary stearic acid does not raise plasma cholesterol.