text: The proposed study intends to continue the investigation of the electrical properties of the mitochondrial membrane using microelectrodes and to initiate studies of the electrical properties of the outer envelope and thylakoid membranes of the chloroplasts. We have found evidence for the absence of a significant metabolically induced membrane potential in mitochondria. Furthermore, the data indicate that in these studies the microelectrode is in the inner mitochondrial space and that the impaled mitochondria are metabolically viable. These results would seem to invalidate one of the mechanisms of oxidative phosphorylation presently considered. We would like to address our studies to the following problems: 1. Further verification of the internal location of the microelectrodes by two methods. 2. Measurement of the internal pH in mitochondria in the presence or absence of metabolism using pH sensitive microelectrodes. 2. A complete study of the electrical resistances of the mitochondrial membranes. We have some preliminary indications that electrical current is carried through the alternative in the study of the permeability of mitochondria to anions. Since anion transport can be inhibited by specific inhibitors, this portion of the study could provide additional evidence for an internal location of the impaling microelectrode. 4. A test and a possible study of whether current injection in mitochondria can produce ATP. 5. A study of the electrical properties of the outer and the thylakoid membranes of chloroplasts using microelectrodes and electrofluorimetric dyes. 6. A study of the effect of illumination on the pH of chloroplasts and of the inner thylakoid space.