Mycoplasmas are most often responsible for respiratory and genital infections. At present, diagnosis is carried out by serology for infections caused by M. pneumoniae and by culture for infections due to genital mycoplasmas. For M. pneumoniae, new prospects may lead to a rapid diagnosis, detection by molecular hybridization and immunological detection. Also, the research of specific antibodies should benefit from a better knowledge of the major antigens. Culture of the genital mycoplasmas, U. urealyticum and M. hominis is simple, but the interpretation of their presence is difficult because they may be recovered in a commensal condition. The envisaged advances should lead to a better assessment of their pathogenicity. The role of M. genitalium, a species related to M. pneumoniae recently discovered in respiratory specimens, should be better determined by sensitive techniques developed to distinguish it from M. pneumoniae.