Marine oil-derived n-3 fatty acids have been shown to stimulate intestinal Ca absorption in animal studies, but the effects of such fatty acids on Ca absorption in human subjects are relatively unknown. In particular, n-3 fatty acids may be of therapeutic value for some Crohn's disease patients who experience Ca malabsorption. Therefore, the aim of the present study was to investigate the effect of 20: 5n-3 and 22: 6n-3 on transepithelial Ca transport across monolayers of healthy Caco-2 cells as well as of TNF-alpha-treated Caco-2 cells (an in vitro model of Crohn's disease). Caco-2 cells were seeded onto permeable filter supports and allowed to differentiate into monolayers, which were treated with 80 mu M-20 : 5n-3, 80 mu M-22 : 6n-3, or 40 mu m-20 : 5n-3 + 40 mu m-22 : 6n-3 for 6 or 8 d, with or without co-treatment with TNF-alpha (10 ng/ml) (n 11 -15 monolayers per treatment). On day 16, transepithelial and transcellular transport of Ca-45 and fluorescein transport (a marker of paracellular diffusion) were measured. Treatment of healthy and inflamed Caco-2 cells with 20:5n-3, 22:6n-3 and both fatty acids combined for 8 d significantly (P < 0.005-0-01) increased total transepithelial Ca transport compared with that in control, effects which were mediated by an enhanced rate of transcellular Ca transport. The effects of n-3 fatty acids on Ca absorption after 6d were less clear-cut. In conclusion, the present in vitro findings highlight the need to investigate the effect of marine oil-based n-3 fatty acids on Ca absorption in vivo in studies of healthy human subjects as well as of Crohn's disease patients..