White adipocytes constitute one of the most important target cells for insulin action to lower blood glucose level in the body. Thiazolidinediones (TZD), a class of new oral hypoglycemic agents, mediate their effect through the peroxisome proliferator-activated receptor g (PPARg), which is highly abundant in adipose tissue. Rosiglitazone is a potent agonist of PPARg and could significantly improve the adipocyte differentiation in 3T3-L1 cells. Application of insulin induces an increase in membrane capacitance (C_m)ofsingle white adipocytes. We wanted to determine: (I) whether the treatment of 3T3-L1 cells by rosiglitazone affects the rate of differentiation and the size of single 3T3-L1 adipocytes, (II) whether changes in C_m of insulin-treated single 3T3-L1 adipocytes exhibit an increases in PM area as shown previously for primary adipocytes, (III) whether activation of PPARg by rosiglitazone significantly alters the specific insulin induced changes in membrane surface area of single adipocytes. We differentiated 3T3-L1 fibroblasts into 3T3-L1 adipocytes and used them for monitoring net changes in PM surface area by the electrophysiological measurements of membrane capacitance (C_m), a parameter linearly proportional to the PM surface area. The presence of rosiglitazone increased the fraction of differentiated 3T3-L1 adipocytes in cell culture vs. controls and significantly reduced the size of single 3T3-L1 adipocytes. Insulin increased the rate of C_m, which was significantly different from controls. Pretreatment of cells with rosiglitazone prior to the treatment with insulin resulted in attenuated rate of Cm increase. In rosiglitazone treated cells, insulin stimulates a rapid increase in exocytosis that is associated with a similar increase in the rate of endocytosis, since both processes appear to be controlled by insulin. Thus secretory function and/or transporter density regulation would be preserved under such condition, while the insulin-induced increase in C_m is attenuated. The current study suggests that activation of PPARg by a competitive PPARg receptor agonist, rosiglitazone, significantly attenuates the specific insulin-induced time-dependent changes in membrane area of single adipocytes.