Cells of in vitro cultured epidermis explants of ectoderm isolated at early gastrula stage, showed only weak excitability or even non-excitable at 6V when examined electrophy siologically. If non-excitable explants were treated with 100 mM glucose, the action potential (AP) appeared and within 1 hr reached its maximum. At the same time, their stimulus threshold became lowered gradually. And, if the glucose was washed out, AP gradually disappeared. If explants were treated with glucose of different concentrations, the percentage of explants which displayed AP increased with the increase of glucose concentration. When explants with approximately the same original stimulus threshold were treated with glucose of different concentrations, the stimulus threshold became lowered more in the more concentrated solution. If explants with different original stimulus thresholds were treated with glucose of the same concentration, the lowering of stimulus threshold was more obvious in those with higher original stimulus threshold. Other energy supplying substances used showed similar effect. Cells of in vitro cultured epidermis explants of ectoderm isolated at early gastrula stage, showed only weak excitability or even non-excitable at 6V when examined electrophy siologically. If non-excitable explants were treated with 100 mM glucose, the action potential (AP) And, if the glucose was washed out, AP was gradually disappeared. If explants were treated with glucose of different concentrations, the percentage of explants which displayed AP increased with the increase of glucose concentration. when explants with approximately the same original stimulus threshold were treated with glucose of different concentrations, the stimulus threshold decreased were in the more concentrated solution. same concentration, the lowering of stimulus threshold was more obvious in those with hig her original stimulus threshold. Other energy supplying substances used showed similar similar.