Experimental immunotherapy with a mixture of allogeneic tumor cells and BCG cell-wall skeleton (BCG-CWS) was carried out against established autochthonous fibrosarcomas induced by 3-methylcholanthrene (MCA) in the subcutaneous tissue of rats. The inhibitory effect on growth in the early stage, tumor-size up to 2 cm in diameter, was significantly observed. No significant difference, however, was shown as compared with the effect of treatment with allogeneic tumor cells alone. That is to say, a more effective inhibition of growth due to the addition of BCG-CWS was not demonstrated.