Over the last few years the possibility of introducing foreign material into the genome of host cells has become technically feasible. This has opened a new era in the treatment of congenital disorders, but has also offered potential innovative avenues in the management of cancer patients. Here, we shall discuss how cytokine genes may be successfully transduced into the DNA of different experimental tumours and how through this approach the tumorigenicity of the neoplastic cells may be abrogated. Emphasis will be given on the demonstration that following cytokine gene transfer, namely with the interleukin 2 (IL-2) gene, two of the primary goals of an optimal immunotherapeutic approach, i.e. anti-tumour specificity and memory, may be achieved. Attention will be focused, in particular, on the results so far obtained, as well as on ongoing studies, with human tumour cells engineered to release different cytokine genes. The design and activation of the first clinical protocols aimed at treating advanced cancer patients with cytokine gene-transduced neoplastic cells will also be discussed, together with other strategies of genetic engineering currently under investigation.