Changes in expression of P2X receptors (P2X1-7) during postnatal development of the rat cerebellum are described. At P3, immunoreactivity (ir) to all the P2X receptors, except for P2X3 receptors, was found in Purkinje cells and deep cerebellar nuclei, P2X5-ir being most prominent. Granular and microglial cells were labeled for P2X5 (weakly) and P2X4 receptors, respectively. At P7, expression of all the P2X receptors (with the exception of P2X3) was up-regulated, P2X5 and P2X6 receptors being most prominent. Scattered P2X receptor-ir in unipolar brush cells in the granular cell layer and P2X1- and P2X7-ir of microglial cells was also present. At P14, the dendritic trees of Purkinje cells were intensely labeled by P2X1-7 receptor antibodies, except for P2X3, while P2X1, P2X4 and P2X7 receptor immunostaining in microglial cells and P2X5 receptor immunostaining in granular cells was up-regulated. At P21, expression of all P2X receptors (except P2X3) was down-regulated in the Purkinje cells and deep cerebellar nuclei; P2X1, P2X4 and P2X7 receptors-ir was present in microglial cells. In contrast, expression of P2X5-ir in granular cells was up-regulated. At P60, expression levels of all the P2X receptors (except P2X3) were similar with those at P21. In double-labeling experiments, almost all the P2X-ir Purkinje cells were immunoreactive for calbindin-D28k, while 60-80% of P2X-ir cells in the granular cell layer were immunoreactive for calretinin. The possible short- and long-term functional significance of the changes in expression of P2X receptors during postnatal development is discussed.