We have reported that patients with metastatic melanoma treated with an autologous, dinitrophenol-modified vaccine develop inflammatory responses at tumor sites. Histologically, these inflamed lesions are characterized by T cell infiltration, which is sometimes associated with tumor cell destruction. We tested biopsy specimens of eight subcutaneous metastases that had developed inflammation following vaccine treatment for expression of mRNA for interferon gamma (IFN gamma), interleukin-4 (IL-4), tumor necrosis factor alpha (TNF alpha), and IL-10. Post-vaccine, inflamed biopsies contained mRNA for IFN gamma (5/8), IL-4 (4/8) or both (3/8), and for TNF alpha (4/7). In contrast, IFN gamma mRNA was detected in only 1/17 and TNF alpha mRNA in 2/16 control specimens (pre-treatment lymph node metastases or non-inflamed subcutaneous metastases). mRNA for IL-10, a cytokine with anti-inflammatory properties, was detected in 24/25 melanoma metastases and was independent of lymphoid content; in situ the reverse transcriptase/polymerase chain reaction confirmed that melanoma cells were the major source. These findings may provide a new parameter by which to measure the effects of cancer immunotherapy.