Flow cytometry was used to demonstrate that cultured human melanoma BRO cells expressed membrane-bound tumour necrosis factor-alpha (TNF-α) and were able to release TNF-α upon treatment with glucosaminylmuramyl dipeptide (GMDP). The released TNF-α was shown to prime melanoma cells, previously unable to respond to GMDP by increasing expression of melanoma-associated antigens, making them sensitive to GMDP treatment.