Cytochrome of the f type was isolated from the thermophilous autotrophic strain Chlorella pyrenoidosa Pringsheim 82T and purified on Sephadex G-75. The isolation procedure allowed a simultaneous production of glutamate dehydrogenase isoenzymes. From 100 g of Chlorella wet paste 100 to 120 nM of electrophoretically unicomponent protein with a molecular weight of 12,000 to 13,000 were isolated. The Chlorella cytochrome had an absorption spectrum in the visible light that was typical of the f type cytochromes.