We used DiOC6(3) to stain the ER in frog A6 cells and observed the fluorescence by time lapse. We saw that the ER was moving retrogradely at a steady slow rate of about 0.3 Ám/min. Latex beads were dropped onto the cell surface in order to observe the retrograde cortical flow. DiOC6(3) stains the beads lightly, allowing us to observe the retrograde movements of both ER and beads at the same time. Both moved at the same rate, showing that the ER is tightly coupled with the retrograde movement of the cell cortex. movie 239K. (Images taken at about 90 sec intervals; the first and last images are scanning DIC images, showing the position of the beads). The effects of nocodazole, taxol and cytochalasin were also observed. We discuss how microtubule dynamics, motor elongation of ER along microtubules, and retrograde cortical movements could interact to give rise to the distribution of microtubules and ER in lamellipodia.