We here summarize the analysis of 126 DNA samples from patients with hematopoietic neoplasias and solid tumors and from various tumor cell lines that were screened in the tumorigenicity assay. Thirty-eight samples were able to induce tumors after transfection in NIH/3T3 cells and injection into nude mice. Southern-blot analysis with a panel of oncogene probes revealed human ras genes in the vast majority of cases (25 N-ras, 2 K-ras, 1 H-ras) but also activated FGF4, dbl, ret and mas genes respectively. DNA samples from the 6 remaining transfectants were cloned into EMBL-3 phages and screened with a human specific repetitive Alu probe. Direct hybridization of a transfectant cDNA library allowed cloning of the ufo oncogene. Application of the exon-trapping technique to alu-positive phage DNA from the other transfectants enabled us to isolate tre, cot, B-raf, p85beta/HUMORF8 and a novel oncogene.