Experimental tuberculosis in mice infected with streptomycin-resistant Mycobacterium tuberculosis SCHACHT strain was treated with streptomycin or rifampicin alone and in combination with schizophyllan. The histopathogical tests of various organs of the treated mice were carried out. 1) In the group of mice treated with streptomycin alone, the moderate focal proliferation of RE cells were seen at the beginning of infection. However, durable activation of RE cells and the prolongation of life-span could not be recognized as compared with control animals. 2) The treatment with streptomycin-schizophyllan combination appeared to be somewhat more effective than schizophyllan alone, the phagocytic capacity being more strongly stimulated. 3) In the group treated with rifampicin alone, the therapeutic effect could be exhibited by the direct antibacterial action of rifampicin, but the activation of RE cells was slight. When rifampicin was discontinued, the growth of tubercle bacilli was rapidly resumed, and the durable therapeutic effect seemed not to be expected. Degeneration of hepatic cells tended to develop. 4) In the group treated with rifampicin-schizophyllan combination, the antibacterial effect of rifampicin appeared to be potentiated by the strong activation of RE cells by schizophyllan, showing the durable therapeutic effects.