Studies on the biochemical and molecular mechanisms underlying obesity have shown that the expression of some proteins was decreased with obesity in rat adipose tissue. One of these proteins is carbonic anhydrase III (CA III) which constitutes 24% of the cytosolic protein content and its function is unclear. A freshly isolated rat adipose cell culture model was used to examine the effect of leptin and insulin on CA III expression. It was found that leptin decreased CA III expression while insulin increased it which suggests that the decrease in CA III expression observed in obesity in rat adipose tissue may be related to hyperleptinemia.