The activation of P2-receptors has a wide range of diverse effects in many tissues. Here we show that extracellular ATP stimulates lipogenesis in adipocytes derived from the epididymal fat pads of male Wistar rats. The lipogenic effect of ATP is not susceptible to treatment of adipocytes with adenosine deaminase or an adenosine receptor antagonist. Degradation of ATP in adipocyte suspension by ectonucleotidases is slow and remaining ATP concentrations are sufficient to activate P2-receptors. ATP does not affect basal or insulin stimulated glucose transport, or basal or isoproterenol stimulated lipolysis, respectively. The lipogenic effect of ATP is mimicked by the adenine compounds, ADP, AMP, and beta,gamma-methylene-ATP, but not by other nucleotides (UTP, UDP, CTP, GTP, ITP, and diadenosine tetraphosphate), indicating that extracellular nucleotides stimulate lipogenesis via a P2-receptor. ATP and its receptor may define a signalling system in adipocytes, which regulates fat stores independently from established hormones.