Reticulated platelets (RP) retain some residual mRNA in their cytoplasm and are thought to be the most recently produced platelets in circulation. They can be visualized on a blood film with new methylene blue staining. RP is a flow cytometric assay utilizing a fluorescent dye, either thiazole orange or auramine O. There is a difference in reference values for RP between thiazole orange and auramine O. From the analytic results of RP in patients with thrombocytopenic disorders, RP measurement is considered useful for estimating thrombopoiesis in bone marrow and for differential diagnosis and elucidating the pathophysiology of thrombocytopenic disorders. In the future, test for RP might have a possibility of routine examination because RP can be rapidly and simply measured using whole blood stained with auramine O using an automated reticulocyte counter modified to determine RP. Furthermore, it is anticipated that standardization and morphological definition for RP are established and accuracy for RP is improved.