Broader application of adoptive transfer of tumor-specific T-lymphocytes is accompanied by the need for effective suicide genes to ensure the safety of this cell-based therapy. In vivo elimination of T-lymphocytes expressing the herpes simplex virus-derived thymidine kinase gene has demonstrated the feasibility of this suicide gene as safety switch. However, improvements are required to overcome initial problems, such as immunogenicity. Here, newly developed suicide genes, including inducible Fas, inducible caspase and CD20 are discussed. In addition, problems of clinical application of marker genes and gene transfer techniques, which are prerequisites for suicide gene therapy, are addressed.