The association of phosphorylation and the reduction of an electron acceptor such as ferricyanide increase similarly with the addition of phosphate, magnesium (Mg), and ADP. The existence of these three components is important for maximal reductive and phosphorylative activity. Similar increases in the rate of ferricyanide reduction can be stimulated by a dilution technique. Dilution does not cause a further increase in the rate in which ferricyanide is reduced with the accumulation of ADP, phosphate, and Mg to a treated chloroplast suspension. ATP inhibits the rate of ferricyanide reduction. Studies of light intensities revealed that the effect was largely on the light-independent steps of the Hill reaction. These observations are explained in terms of a proposed method in which phosphate esterifies during electron transport reactions, reducing ferricyanide, while the rate of electron transport is limited by the rate of phosphorylation. An increase in the rate of phosphorylation increases the rate by which electrons are transported in the electron transport system.