Close relationships have been demonstrated between adipose tissue and the inflammatory/immune system. Furthermore, obesity is increasingly considered as a state of chronic inflammation. Cytofluorometric analysis reveals the presence of significant levels of lymphocytes in the stroma-vascular fraction of white adipose tissues. In epididymal (EPI) fat, lymphocytes display an "ancestral" immune system phenotype (up to 70% of natural killer (NK), gammadelta+ T and NKT cells among all lymphocytes) whereas the inguinal (ING) immune system presents more adaptive characteristics (high levels of alphabeta+ T and B cells). The percentage of NK cells in EPI fat was decreased in obese mice fed with a high-fat diet, whereas gammadelta positive cells were significantly increased in ING fat. These data support the notion that adipose tissue may elaborate immunological mechanisms to regulate its functions which might be altered in obesity.