Inulin space was measured in the normal control rabbits and abdominal vena cava partially ligated (to about 1/2 of normal lumen) rabbits. Eleven rabbits served as the control and 12 rabbits after 7 to 10 days of abdominal vena cava ligation were used. Inulin space in the normal rabbits was 376±102.70 ml (Mean±S.D.) or 18.0±5.21% body weight. After 7 to 10 days of abdominal vena cava partial ligation inulin space decreased and the values were; 253±145.79 ml or 14.4±8.55% body weight.