Exposure to red and blue lights caused an increase in electrical currents ($0.14{mu}A;cm^{-2}$ for red and 0.05${mu}A;cm^{-2}$ for blue, respectively) flowing on the lower surface of leaves from Commelina communis. However, no changes were measured in currents from isolated epidermal cells. To determine the influence of the mesophyll on such electrical changes, those cells were infiltrated with photosynthesis inhibitors. Both DCCD treated and control leaf discs showed the same level of response to red light. Epidermal strips were also removed to measure the ruvrents above partially exposed mesophyll tells in order to elucidate the relationship between intact leaves and those mesophyll cells. Changes in current were smaller in the latter type. The partially exposed mesophyll cells of a leaf also showed electrical current changes, but smaller than those of the intact leaf. In DCMU-infiltrated leaf discs, the electrical currents of intact leaves were increased to $0.05{mu}A;cm^{-2}$ in response to red light. for sodium azide-infiltrated leaf discs, however, intact leaves showed no response. Likewise, a measure of photosynthetic efficiency, the Fw/Fm ratio, was reduced to that measured in the control, thereby indicating that photosynthetic activity significantly altered the electrical current for intact leaves. Therefore, these results demonstrate that the current observed from the lower side of intact leaves is related to photosynthetic activity in the mesophyll cells.