Amidated alginates (octadecylamides of alginic acid) are efficient sorbents of lipids. In the present study amidated alginates were prepared from sodium alginate of low and medium viscosity. Both amidated alginates were active in the removing of dietary fat from the body of rats. The highest daily output of faecal fat was observed in rats fed amidated alginate prepared from Na-alginate of low viscosity. The lowest hepatic concentration of cholesterol and the lowest faecal output of bile acids were observed in rats fed amidated alginate of medium viscosity. Aminotransferases AST and ALT were not significantly influenced.