The use of whole cell tumour vaccines in the treatment of malignant melanoma has given mixed results. Cytokine-transfected tumour cells as vaccine have shown efficacy in animal models but need to be compared with other means of enhancing a systemic anti-tumour immune response. A new generation of immunological adjuvants claimed to be more effective than the conventional adjuvants is now available for assessment. We have investigated the action of an oil-microemulsion adjuvant formulation (IDEC antigen formulation (IDEC-AF)) in the B16-F10 murine melanoma model. After standardisation of the whole cell tumour vaccination protocol we showed that mice vaccinated with whole irradiated cells combined with IDEC-AF produced a significant inhibition of tumour growth, following a challenge with live tumour cells, when compared with mice vaccinated with whole cell vaccine alone. IDEC-AF was superior to two conventional adjuvants, namely alum and incomplete Freund's adjuvant and a more reliable response was achieved with the oil-microemulsion adjuvant compared with IL-2-transfected cells. In addition, the adjuvant was comparable in efficacy to IL-4-transfected B16-F10 cells. Given the practical difficulty in using cytokine-transfected tumour cells and the limited therapeutic range of some cytokines, a cheap and easy to deliver adjuvant formulation proved equally or more effective than some of the currently clinically used transfected cytokines.