The growth of Mycoplasma hominis is stimulated by arginine. A possible mechanism for degradation of this amino acid is the arginine dihydrolase pathway. The first enzyme of the pathway, arginine deiminase, is inducible in M. hominis. Evidence exists that the dihydrolase pathway is not the major pathway to production of adenosine triphosphate in the organism. M. hominis does not take up nucleosides from the growth medium, although the metabolic processes required for the transformation of precursors into nucleic acids are present. The system by which L-methionine is transported across the cellular membrane of M. hominis resembles the active-transport systems found in other microorganisms. The membrane of M. hominis contains a high level of cholesterol in the unesterified form. The low-density fraction of human serum lipoprotein is an effective cholesterol donor, as are cholesterol-phospholipid liposomes with a high cholesterol content.