Dikegulac sodium foliar spray treatments of up to 500 mg/liter resulted in temporary arrest of apical development in Zinnia, Helianthus, and Chrysanthemum. Leaves expanding directly after treatment were convoluted and chlorotic but later greened. Later-developing leaves were irregularly shaped and green. There was some outgrowth of axillary buds. Histoautoradiographic studies showed that DNA synthesis was inhibited throughout the apical meristem, and normal cytohistological zonation was no longer apparent. In axillary buds DNA synthesis was detected. Whole plant autoradiography showed that dikegulac applied to a leaf was translocated to the apex. We suggest that dikegulac acts selectively on meristematic cells in the apex and developing leaf primordia and that minute amounts of the agent are sufficient to effect changes in apical development. Thus, we concluded that dikegulac probably acts "hormonally" on the apex, unlike X-irradiation and other chemical pinching agents.