Stamen hair cells of Tradescantia virginiana have been microinjected with p13suc1 labeled with carboxyfluorescein (CF) and studied throughout the division cycle in living cells by using the confocal laser scanning microscope. The protein, p13suc1, is essential for the rapid inactivation of the key mitotic catalyst, p34cdc2 kinase, at anaphase and for completion of nuclear division. During interphase or prophase, CF-p13suc1 concentrates quickly (< 2 min) in nuclei, reaching levels that are approximately 2-fold greater than those in the cytoplasm. At nuclear envelope breakdown, CF-p13suc1 permeates throughout the entire spindle and nonspindle cytoplasm. The protein is excluded from the tightly condensed chromosomes but otherwise no regions accumulate or exclude the protein. It remains evenly distributed throughout metaphase, anaphase, and well into cytokinesis; however, during telophase CF-p13suc1 reconcentrates in the daughter nuclei.