The effect of dietary pectin and algin on hepatic lipogenesis in rats was studied in vivo and in vitro. The biosynthesis of cholesterol, as measured by conversion of acetate-1-C14 to cholesterol was substantially higher in the experimental groups in vivo and in vitro. The incorporation of label into triglycerides and hospholipids and into total lipids was found to be significantly lower in the pectin-fed group in the in vivo study and significantly higher in the in vitro study. The results indicate that pectin interferes with absorption of the various lipids. The significance of these observations is discussed. The differences between the algin-fed group and the controls were not always significant.