A single oral administration of 27 mg 11-H-eicosafluorundecanoic acid/kg of body weight (according to 1/20 of the oral LD50; 0.049 mM) resulted in a long lasting hepatomegaly in male rats. This was accompanied by a decrease of the triglyceride and total lipid levels in blood serum, a temporary increase of the total lipids in the liver, and an increase of the hexobarbital sleeping time, the latter being normalized before the liver/body weight ratio reached the control level. The bromothalein elimination and the S-alanine amino transferase and S-alkaline phosphatase activities were not affected.