The use of recombinant interleukin 2 (rIL‐2) in clinical practice has opened up new and beneficial avenues in the treatment of certain malignant diseases. Although rIL‐2 can stimulate a range of host antitumour defence mechanisms, only 30–40 per cent of patients who are treated will respond to such therapy as assessed by a reduction in tumour volume. The effect of rIL‐2‐based treatment schedules on delaying progression of disease and on overall survival in comparison with standard current treatments and chemotherapeutic regimens is not clear. Randomized clinical trials are required to evaluate precisely the role of rIL‐2 in various therapeutic combinations and to ascertain the optimum therapeutic regimens for individual tumour types. Studies currently under way should provide more insight into the possible beneficial effects of immunotherapy with rIL‐2. More basic research is required to ascertain how rIL‐2 may produce its antitumour effects and why the therapeutic results obtained in humans have been so selective and less beneficial than those in experimental animals.