Three kinds of non-identical subunits were found to be present in carbon monoxide dehydrogenases from Pseudomonas carboxydohydrogena (85,000, 28,000, and 14,000) and Pseudomonas carboxydovorans (85,000, 25,000, and 14,000). The subunit pattern of these enzymes was constant and was not changed either by analysis of the enzyme under different conditions or by inducing the enzymes under variable culture conditions.