The effect of prodigiosan, levamisole and methyluracil on the number of endogenic colonies in the spleen and absorptive function of the reticuloendothelial system (RES) was studied comparatively in intact mice and mice treated with prednisolone, cyclophosphamide and chloramphenicol. It was shown that prodigiosan stimulated the endogenic colony formation with all the administration schemes in both the intact animals and the animals treated with chloramphenicol. The stimulating effect of methyluracil was observed, when it was used prophylactically. The effect of levamisole was not consistent. A significant stimulating effect of prodigiosan on absorptive function of the RES in the intact animals and the animals treated with prednisolone was shown. Methyluracil increased absorption of staphylococci by the macrophages in the intact animals. The effect of levamisole on the intact animals was not observed, while in the animals treated with prednisolone and cyclophosphamide it stimulated the absorptive capacity of the RES. Levamisole did not change the effect of prodigiosan and methyluracil on endogenous colony formation when used therapeutically, prevented the prodigiosan effect and potentiated the effect of methyluracil on absorptive function of the RES.