BACKGROUND: There has been a substantial increase in our understanding of the pathogenesis of cancer over the past decades, and new treatment modalities are being developed on the basis of this knowledge. MATERIAL AND METHODS: The literature is reviewed, and the status of gene therapy protocols approved in Norway is presented. RESULTS: About 70% of the more than 400 clinical gene therapy studies started are targeted at cancer. Several different principles are used, including gene therapy targeted at tumour suppressor genes, oncogenes, or central signaling molecules, as well as "suicide gene" therapy. In addition, various gene therapy protocols aim at strengthening immune responses. Most studies have been early clinical trials primarily designed to study safety, applicability and toxicity. Several of these phase I and II studies have, however, shown partial remission of tumours and, in rare cases, complete remission, although curation has not yet been shown. In some trials, including TP53 gene therapy trials, effects on tumour size have been observed in up to 50% of the patients. Up until now, only two phase III and one phase II/III studies have been initiated, but results from these studies have not yet been published. The two first gene therapy protocols approved in Norway are also targeted at cancer. So far, six patients in Norway have undergone gene therapy. INTERPRETATION: As of today, the results should be seen as promising for some of the principles which are being tried out; their clinical importance must, however, be documented in larger controlled clinical trials.