In an attempt to examine the functions of the RES by assimilate colloids other than iron colloids, linoleic acid-(14)C emulsion and lipid emulsion, fatgen, were selected and by treating the RES of the dog with these emulsions observations were carried out on the behaviour of the RES functions at the surgical intervention. The results of the study are briefly presented in this communication. 1. It was fund that linoleic acid (14)C-emulsion is taken up by the RES, is soon saturated, and readily incorporates into fat tissue. For the study of the RES function in animals this is a very usefuly method with a promising future. 2. The lipid emulsion fatgen is taken up and metabolized readily by the RES, proving that the treatment of RES by this emulsion can take place of Congo red method in the clinical examination of the RES. 3. For the examination of the function of the RES of experimental dogs at surgical operation the treatment by the lipid emulsion gives somewhat different results in detail compared with the Glycyrrhizin acid iron colloid, but in the case of splenectomy the compensatory function of the residual spleen is markedly accelerated and the liver in the splenectomized group compensates the removal of spleen, indicating that both methods yield similar results on the whole. From these findings it seems that the lipid colloid method as well as the Glycyrrhizin iron colloid method are to be highly recommended as the new, excellent methods to be applicable to clinical examinations of the RES functions.