The performance of the complement fixation test for amoebiasis has not been sufficiently reliable to establish its general use in the diagnosis of this infection. The limiting factor of greatest concern has been the inadequacy of the antigen due in part at least to numerous undetermined species of bacteria and their metabolic products which have occurred in the cultures of the specific organism used for antigen production. Furthermore, the flora has no doubt varied in each successively cultivated strain of Endamoeba histolytica. In the presence of such unstable and undetermined factors, various investigators have not accomplished the production of antigens of uniform quality. In general, attempts to purify the antigen by washing the trophozoites free from the associated flora have not provided an answer to the problem of specificity. For these reasons efforts have been made in this laboratory to cultivate the amoeba without bacteria.