Interleukin 2 (IL2) production is known to bypass T-helper-cell function in the generation of an antitumour response. The present analysis was designed to assess the effects of application of renal cancer vaccine with and without IL2 on delayed-type hypersensitivity (DTH) skin responses to the vaccine itself and tumour cell challenge. The renal cancer vaccine consisted of Newcastle disease virus (NDV)-infected autologous irradiated tumour cells and topical application of low-dose rIL2 (75,000 Cetus units). As a result, the coadministration of a supplement of rIL2 proved to be important for augmentation of DTH responsiveness to tumour cell challenge. Patients with aneuploid tumours vaccinated without rIL2 developed an anergy to the vaccine throughout vaccination. This effect could be reversed by the topical coapplication of this cytokine. While the treatment of renal cancer patients with IL2-based immunotherapy regimens appears to be effective in advanced renal cell carcinoma the IL2-supplemented vaccines should be tested to assess their benefit in the situation of "minimal disease" after surgery especially in high-risk patients with aneuploid tumours.