Visfatin, a novel adipocytokine preferentially expressed in omental (Om) adipose tissue (AT), has been shown to exert insulin-mimetic effects in mice and humans. Recent studies in Asian populations show elevated serum visfatin levels in subjects with Type 2 Diabetes Mellitus (T2DM), suggesting a potential role for visfatin in the pathogenesis of this disease. Whilst central adiposity is closely related to IR and T2DM, the role of AT in the development of these conditions remains unclear. Therefore for this study we investigated circulating levels of visfatin in Caucasian non-diabetic (ND) and diabetic (DB) subjects (DB BMI:35.9(mean±S.D.)±7.2 kg/m2; Age:56.0(mean±S.D.)±9.8 yrs, n=36; ND BMI:26.0±2.7 kg/m2, Age:38.9±12.9 yrs, n=23). Our studies demonstrated that the T2DM subjects exhibited higher serum visfatin levels compared with ND controls (DB: 21.8±3.6 ng/ml, ND: 13.9±1.5 ng/ml, P<0.05). Secondly we examined serum visfatin levels in T2DM patients pre- and post-RSG treatment (BMI:36.1±7.0 kg/m2; Age:57.8±11.2 yrs, n=8). Post-RSG treated diabetics showed a significant reduction in circulating visfatin and insulin levels compared with pre-treated subjects (pre-RSG:10.77(mean±S.E.M.)±1.47 ng/ml; post-RSG:7.45±1.60 ng/ml, P=0.04). We then investigated the ex vivo depot specific expression of visfatin in human AT (abdominal subcutaneous (AbdSc) n=11, Om n=11 and thigh n=6) which showed that visfatin protein is expressed in a depot specific manner (Om>AbSc>Thigh, P<0.01). Finally we studied the effect of insulin alone and in combination with the insulin sensitiser, rosiglitazone (RSG) on visfatin in isolated human AbdSc adipocytes. This determined that RSG 10 nM/insulin100 nM reduced visfatin protein expression compared with insulin alone (P<0.001). In summary, visfatin is expressed in a depot specific manner in human AT. Furthermore, RSG reduces visfatin protein expression in AbdSc adipocytes, as well as circulating levels in T2DM patients. These data indicate that elevated visfatin levels are a feature of T2DM and are regulated by insulin. The finding that RSG lowers serum visfatin in diabetics may contribute to the functional effects of this anti-diabetic agent.