Cells of the superficial layer which had been explanted from the presumptive ectoderm of Rana japonica early gastrulae at stage 10 differentiated into cement-gland cells (CGCs) when cultured in Barth's solution containing 90-130 mM-NaCl, and into common epidermal cells and cilia cells when cultured in a solution containing 20-40 mM-NaCl. They failed to differentiate, however, when cultured in a solution in which NaCl is 15 mM or lower. The optimum condition for inducing the differentiation of CGC was stimulating them with a solution containing 130 mM-NaCl for 6-10 h at 18 degrees C, followed by culturing in a solution containing 15-40 mM-NaCl for 7 days. The greatest ability to react to the CGC-inducing stimuli resided in the superficial layer of the presumptive ectoderm of the embryo at stages 10-11. Under the optimum condition, the total volume of CGCs induced amounted to about 85% of the explanted tissue. High percentage comparable to this was obtained with stimulation by KCl, RbCl, sucrose or mannitol.