There is a growing list of possible tumor suppressors that can potentially be used to control cancer cell growth in the clinic. These include p53, Rb, p21, p16, p27, BRCAI and APC, some of which are already in clinical trials, p53 induces apoptosis and suppresses cancer cells containing multiple genetic alterations as well as multidrug-resistant cells, making it a promising and popular target. Other agents such as CDK-inhibitors are generally cytostatic with little evidence for apoptosis. The genetic make-up may help guide a rational therapy of particular tumors. Preclinical studies are exploring combinations of gene therapy and chemotherapy. Some early results are beginning to emerge from clinical trials including those using the E1b-deleted adenovirus that is unique in being a tumor-specific cytotoxic agent for the most common types of cancer.