Bladder carcinoma associated with leukemoid reaction, though it rarely occurs, is considered highly malignant and has proved to produce granulocyte colony-stimulating factor (G-CSF). Interest exists in whether G-CSF itself or G-CSF producing ability reflects the malignant potential of such a tumor, possibly through an autocrine mechanism. In a patient with invasive bladder carcinoma, we found that the tumor cells produced G-CSF responsible for a remarkable leucocytosis. However, we could not detect the rearrangement and amplification of the G-CSF gene nor the expression of G-CSF receptor in the tumor cells. Our immunohistological and molecular biological study failed to demonstrate a crucial role for G-CSF in mediating a growth advantage for the tumor.