We conducted a study of the cell cycle of coconut palm tissues cultured in vitro in order to regulate regeneration. Coconut palm is a plant for which it is difficult to monitor the ability of the meristematic cells to actively divide. Cell nuclei were isolated from various types of coconut palm tissues with and without in vitro culture. After the nuclei were stained with propidium iodide, relative fluorescence intensity was estimated by flow cytometry. Characterization of the cell cycle reinforced the hypothesis of a block in the G0/G1 and G1/S phases of the coconut cells. A time-course study carried out on immature leaves revealed that this block takes place gradually, following the introduction of the material in vitro . Synchronization of in vitro-cultured leaves cells using 60 microM aphidicholin revealed an increase in the number of nuclei in the S phase after 108 h of treatment. The significance of these results is discussed in relation with the ability of coconut tissue cultured in vitro to divide.