Cell size and mitotic index were decreased with increasing concentrations of growth regulators such as GA 3 , uniconazole, chlorocholine chloride (CCC) and 2,3,6-TBA while nuclear volume, interphase chromosome volume and abnormalities were found to increase during division of onion root tip cells. Formation of chromosome fragments, bridges, laggards, single and multiple chromatid bridges, irregular distribution and unequal separation of chromosomes were visualized as the main effects due to the application of these growth regulators.