1. The amounts of tissue lipids were higher in S. etruscus than in C. russula. 2. The level of liver phospholipids was specially low in C. russula, 2650 mg/100 g as opposed to 3725 g in S. etruscus. 3. This is in good agreement with a reduced rate of the labelled acetate incorporation into the lipids of C. russula. 4. The proportion of unsaturated fatty acids was greater in the liver of S. etruscus; however, the percentage of arachidonic acid was higher in C. russula--15% as opposed to 8%.