Proto-oncogenes, which have been widely implicated in the pathogenesis of malignant human tumors, frequently demonstrate restriction fragment length polymorphism (RFLP). Population studies of such restriction alleles is of potential interest for genetic analysis of cancer susceptibility. Some of the initial date of Krontiris et al (1985) showing a significant increase of rare c-ha-ras-l alleles in individuals with tumors, have been confirmed in certain types of cancer (breast cancer, lung adenocarcinoma), whereas others have been refuted (myelodysplasia, melanoma, colon adenocarcinoma). Other significant associations have been found between other proto-oncogene RLFPs and tumors (c-mos and breast cancer, c-raf and non Hodgkins lymphoma, L-myc and lung carcinoma metastasis). Although they are controversial, these studies should be extended, in order to determine whether the presence of certain alleles is a contributing factor in the development of certain tumors.