It is sometimes necessary, particularly in a fine needle biopsy where there is limited histological material for examination, to distinguish BAT cells in a hibernoma from ‘BAT-like’ neoplastic/non-neoplastic cells with vacuolated/foamy cytoplasm in other lesions; our findings showing an absence of expression of specific epithelial, melanoma, leucocyte, macrophage and other markers by BAT cells (taken with expression of aP2/FABP4 and UCP1), are of diagnostic utility in this regard. This evidence concerns the gene FABP4 and melanoma.