Abstract: The present study was designed to investigate the ultrastructural alterations of the peripheral blood lymphocytes of rats exposed to lead. For this purpose, a group of 10 male Wistar albino rats received lead as 0.25% lead acetate trihydrate in drinking water for six months. Blood samples were collected from all experimental animals to separate buffy coats which were processed for electron microscopy. Lymphocytes of the exposed animals revealed obvious fine changes which included nuclear and organellar changes. The lymphocytes nuclei showed deep invaginations of the nuclear envelope and marked chromatin condensation. Mitochondria disclosed swelling and deterioration of their cristae. Rough Endoplasmic Reticulum (RER) was markedly dilated and proliferated in considerable number of lymphocytes. It is concluded that lead can induce significant ultrastructural changes in the peripheral blood lymphocytes. The demonstrated changes may adversely affect the lymphocytes functions which are greatly concerned with the immune status of the exposed subjects.