The kinetics of absorption of L-methionine-methyl-C14 by Hymenolepis citelli were studied using short term incubations. The absorption was shown to follow saturation kinetics. No significant differences were shown between the L- and D- forms of methionine absorption. Fifteen amino acids were found to be inhibitors of methionine absorption. This inhibition was demonstrated to be competitive in nature. Inhibition constants were calculated for all the inhibitors. It was shown that a mixture of amino acids produced a competitive inhibition of methionine-methyl-C14 absorption which could be predicted from the inhibitions produced by the individual amino acids (by the equation of Read et al, 1962, J. Parasit. 48:46 abst.). It is suggested that an amino group alpha to the carboxyl group and a non-polar side chain are the requirements for absorption in this system under the conditions tested. The results are discussed briefly in terms of the ecology of H. citelli.