Depolymerizes microtubules and blocks mitosis at metaphase. Often in karyotyping and cell cycle research it is desirable to increase the yield of mitotic cells in a particular phase of the cell cycle. This can be achieved in a variety of ways with the most popular being the use of a cell cycle synchronizing agent such as demecolcine. Demecolcine will arrest cells in metaphase with no remarkable effect on the biochemical events in mitotic cells or in synchronized G1 and S phase cells. White blood cells are often treated with demecolcine to arrest cells in metaphase.