The spent medium from cultures of the chemoautotrophFerrobacillus ferrooxidansgrown in a ferrous iron – salts medium was examined for organic compounds. Pyruvic acid was identified by chromatography after precipitation of the iron salts, and was determined at various times during the culture growth cycle. Analyses of the spent medium from cultures grown in the presence of C14O2indicated that a large portion of the CO2fixed by the organism was released into the medium. A significant portion of the radioactivity in the medium could be extracted as the 2,4-dinitrophenylhydrazone derivative. Very little radioactivity was extracted by ether, indicating that phospholipids are probably not released into the medium by this organism.