Three types of interferon preparation (<latex>$\alpha$</latex>, <latex>$\beta$</latex> and <latex>$\gamma$</latex>) have been used in the treatment of tumours in vivo. At the time of writing no information is available on IFN-<latex>$\gamma$</latex> treatment of tumour patients. Treatments with IFN-<latex>$\alpha$</latex> and IFN-<latex>$\beta$</latex> have been undertaken at many clinical centres. Both types of preparation can exert side effects. Both types have also been able to cause regression of certain tumours in individual patients. At our hospital, IFN-<latex>$\alpha$</latex> has been given to tumour patients over the last decade. Antitumour effects have been registered on patients with juvenile laryngeal papillomatosis, Hodgkin's disease, myelomatosis, ovarian carcinoma, hypernephroma and glioblastoma. Further study is needed on how therapy with IFN should best be undertaken and also how such treatment compares with other treatments of various tumour diseases. IFN therapy should also be combined with other such treatments.