Abstract: Application of fluoroqinolone derivatives of general formula (I) is taught, in which R.sub.1 is alkyl (1 to 4C), fluoroethyl, cyclopropyl or difluorophenyl, R.sub.2,R.sub.3 and R.sub.4 are identical or different and represent hydrogen atoms or methyl radicals, X is N or a group .dbd.CR.sub.6 in which R.sub.6 is a hydrogen or fluorine atom, or alternatively R.sub.6 with R.sub.1 and the atoms to which they are attached forms a six-membered heterocycle substituted with a methyl radical and containing an oxygen atom, and R.sub.5 is a hydrogen atom, or represents an amino radical if R.sub.6 is a fluorine atom, as well as of their salts, for obtaining a medicinal product intended for the preventive and/or curative treatment of pneumocystosis.