The absorption of three amino acids (leucine, alanine and lysine) from the
washed, closed rumen was studied in a short-term (75 min) experiment in sit
u. The concentration of leucine and alanine did not change in the rumen dur
ing the experiment, while that of lysine continuously decreased, and 40% of
the total lysine placed in the rumen was absorbed during the experimental
period. The rate of absorption decreased in proportion to the fall of amino
acid concentration.