Summary of informal discussion of experimental approaches.

from such tumors. Only limited attempts have been made to evaluate tissues from other diseases that are associated with lymphoreticular proliferation. Results with acute phase, mononuclear cells from one case of infectious mononucleosis were negative, but this finding obviously needs confirma tion by study of additional cases. Carcinomas of various origins (e.g., lung, stomach, colon, rectum, ovaries) and brain tumors were positive for oncornavirus information. Studies with cervical carcinomas, which were studied only recently, and a case of sarcoidosis are still incomplete, and lepromatous leprosy has not been studied. To questions by Dr. Goodheart, Dr. Spiegelman replied that he has not yet examined animal tumors caused by herpesviruses but that such studies are planned. Dr. Deinhardt asked whether any checkerboard hybridi zations between murine leukemia, murine mammary tumor, feline, and other mammalian C-type viruses had been per formed and if much overlap was found. This would be im portant because apparently in some experiments much less cross-hybridization was found between nucleic acids of hu man tissues and feline C-type viruses than had been re ported for murine viruses and human tissues; this finding needs clarification. Dr. Spiegelman stated that these spe cific experiments had not been done but such questions would be resolved as work in this area progresses. Probes that are used almost routinely today are made with "par ticles" found in human tissues, and hybridization between