Aberrant expression levels of the ras genes is a common event in human tumors. Transcriptional regulation of the H-rcu proto-oncogene, the most well studied member of the ras family, occurs through nuclear factors that recognize elements in the promoter region of the gene, in the first and fourth intron and in the variable tandem repeat (VTR) region unit and involves alternative splicing and specific methylation patterns, as well. Overexpression of the Ras p21 protein is detected in a variety of human tumors, including neuroblastomas, esophageal, head and neck, laryngeal, thyroid, lung, liver, intestinal, gastric, colorectal, breast, bladder, endometrial, ovarian tumors and leukemias. Levels of the Ras p21 protein are often of great prognostic and clinical significance and controling the expression of ras genes provides a useful target for gene therapy treatments.