Investigation of Fl resistance to parental line tumors will be continued using inbred mice and their hybrids and the relationship between such resistance and the Barrett-Deringer effect will be explored. The importance of the immunological status of the Fl host will be studied. Recent spontaneous tumors will be used to avoid complications due to genetic divergence, acquisition of passenger viruses etc. Studies on effects of neuraminidase on the cell surface will be extended. Approaches in progress include in vivo transplantation studies, serological analysis of antigenicity, cell culture studies of regeneration of sialic acid at the cell surface, provision of material for chemical analysis of cell surface glycoprotein and investigation of a cytotoxic factor in sera from guinea pigs and some strains of mice which reacts with neuraminidase treated tumor cells. Comparison of biochemical and immunological characteristics of 2 sublines of the same tumor, TA3-Ha and TA3-St is also underway.