A method is described for the preparation from green and etiolated tissues of the pea plant, of cytoplasmic particles 'with high oxidative activities in the presence of intermediates of the tricarboxylic acid cycle. The cofactor requirements have been investigated, and for preparations from etiolated pea stems, a phosphorylative ability comparable with animal mitochondria has been obtained. With certain of these preparations an oxidation of butyrate has been demonstrated.