The release of manganese from organic soils by copper has been studied. The results obtained together with the titration curves of acid-washed organic soils, determined in the presence and absence of various added metal ions, support the suggestion of Bremner et al. (1946) that the metals of the first transition series of the periodic table are held in organic soils as complexes. The consequences of the results are discussed particularly in regard to the release of metal ions from soils and their uptake by plants.