In our earlier studies, we have shown that the blocking factor is not an antibody. We are studying further to establish the nature of this blocking factor and the methods by which we could moderate the appearance of this factor. We are proposing to use column chromatography and polyacrylamide slab gel electrophoresis to find out the molecular structure of this blocking factor. Furthermore, to moderate the appearance of this factor, we are using different biological agents, e.g., streptococci. This organism is well adapted to human and animal hosts, and its structure and immune response have been well characterized. Our preliminary studies with streptococcal products have shown the supression of methylcholanthrene induced fibrosarcoma. Using the cytotoxic experiments, we shall be monitoring the appearance or disapprearance of blocking factor in the serum of tumor-induced mice modulated with streptococcal products. BIBLIOGRAPHIC REFERENCE: Bhatnagar, R.M., Zabriskie, J.B., and Rausen, A.A. Cellular immune responses to methylcholanthrene-induced fibrosarcoma in Balb/C mice. J. Exp. Med. 142:839-855, 1975.