Immunofluorescence studies showed that cytoskeletons that were composed of actin and myosin II rapidly reorganized in vegetative Dictyostelium cells upon chemotactic stimulation by folic acid. The amount of F-actin increased biphasically with peaks at 5-10 sec (first peak) and 25-45 sec (second peak) after the addition of folic acid. Filaments of myosin II became associated with cell membrane with increases in the meshwork of actin filaments on the cell membrane at the time of the second peak. The number of actin foci in the actin meshwork on the cell membrane decreased transiently at the time of the second peak. The number of filaments of myosin II on the cell membrane decreased and the number of actin foci recovered concomitantly towards the end of the second peak. This reorganization of cytoskeletons during the chemotactic stimulation was also observed after the application of the calcium ionophore A23187 or cGMP to cells. These observations suggest that increases in intracellular levels of both Ca²⁺ ions and cGMP may play a crucial role in the rapid translocation of myosin II during stimulation by folic acid.