Cytoplasmie particles eOl'l'cspollding to i.he mitochondria of animal and etiolated plant tissues have been prepared from green pea leaves. These part.icles contain t,he complete triearboxylic a(1id cycle ('omplex of enzymes. This has been determined by demonstrating the oxidative and phosphorylative (mpacities of the partieles in the l)I'csence of added snbs/,rates of the trical'boxylie acid cycle, the "sparked" oxidation of pyruvate, the conversion of fumarate to succinate in the presence of malonate', and by the eomplete oxidation of added substrate. lI:nzymes eapable of oxidizing formate, laetate, a number of amino acid,;, Hnd reduced oytoehl'ome c aro looMed in these pnrticles. Diphosphopyridillo nueleotide, triphosphopyridine nucleotide, and sueeinate-linked eytochrome reductases are also present. Tho effeets of varions COf!lctOl's [md inhibitors on the oxidative capaeit.ies of the pm�tielns havo beon ill,-ostigated. Valuos hetwenll :l and :1 for tho ratio of phosphorus esterified to oxygen eOllsumoc! luwe been obtained i'0!' all Hw triem'boxylic acid cy,,]o substrates tested. with til(' exception of succinate, for whieh It value of I ,Ml was found.