Study summary: The current study was designed to investigate the influence of oleic, linoleic and eicosapentaenoic acids on the bioavailability of β-carotene, including plasma β-carotene response and its conversion to retinol (vitamin A). The study was conducted by using single (9 hour time course) and repeated (10 days) dose administrations in rats. After a single dose, the levels of plasma β-carotene and retinyl palmitate in the oleic acid and eicosapentaenoic acid groups were higher by 13, 7 and 11, 6 folds than in the linoleic acid group (p < 0.05). The liver β-carotene level in the oleic acid and eicosapentaenoic acid groups were higher by 3 and 1.2 folds than in the linoleic acid group (p < 0.05). After 10 days' repeated dose, the plasma β-carotene and retinyl palmitate levels in oleic acid (6.2%, 51.7%) and eicosapentaenoic acid (25.4%, 17.23%) groups were higher than in the linoleic acid group (p < 0.05). The liver β-carotene level in oleic acid (21.2%) and eicosapentaenoic acid (17.6%) groups also were higher than in the linoleic acid group (p < 0.05). In both the experiments, the activity of β-carotene 15,15′-dioxygenase in the intestinal mucosa and plasma triglyceride levels were also found to be higher in the oleic acid and eicosapentaenoic acid groups than in the linoleic acid group. β-carotene excreted through the urine and feces of the oleic acid and eicosapentaenoic acid groups was lower than that of the linoleic acid group. The authors conclude that the results demonstrate an improved absorption and metabolism of β-carotene when fed a diet supplemented with oleic acid or eicosapentaenoic acid compared to linoleic acid.