DNA isolated from 19 MCF247 induced tumors in AKR/J mice was studied. A MuLV insert unique to one tumor was cloned from a tumor DNA library in lambda phage. A flanking sequence probe for this cloned tumor MuLV insert was constructed in pBR322 and used to evaluate the other 18 tumors for indications of a common region of MuLV insertion. No evidence for such conditions were obtained indicating that the cloned, tumor unique MuLV may be unrelated to thymoma induction. Isolation of additional MuLV inserts from the tumor DNA library is in progress to continue the study. Evaluation of the 19 tumor DNAs by Southern blot analysis showed that none contained c-myc polymorphisms. Similar studies with other onc probes are in progress.