The invention relates to the use of quinolines having general formula (I), wherein R.sub.1 denotes H; alkyl C.sub.1-C.sub.15; alkenyl or alkynyl C.sub.2-C.sub.15; --CHO; heteroaryl; alkyl C.sub.1-C.sub.15 or alkenyl or alkynyl C.sub.2-C.sub.7 comprising at least one substituent selected from among O, halogen, --OH, --CHO, --COOH, aryloxycarbonyl, alkyloxycarbonyl C.sub.2-C.sub.8, alkenyloxycarbonyl C.sub.3-C.sub.9, nitrile, aryl, heteroaryl, arylsulphone, alkylsulphone C.sub.1-C.sub.7, thioalkyl or aminoalkyl C.sub.1-C.sub.7; alkenyl C.sub.2-C .sub.7 bearing at least one substituent selected from among NH.sub.2, aleoxy C.sub.1-C.sub.7, phenoxy, cycloakyl C.sub.3-C.sub.6 or heteroaryloxy, alkenyl or alkynyl C.sub.2-C.sub.15 comprising at least one trialkylsilyl C.sub.1-C.sub.7; R.sub.2, in position 3, 6 or 8, denotes H; halogen; --OH; --CHO; --COOH; alkyl or aleoxy C.sub.1-C.sub.7; --NH2; alkenyl C.sub.2-C.sub.7; or alkynyl C.sub.2-C.sub.10; R.sub.1 and R.sub.2 do not both denote H. The invention is used for the preparation of a medicine to treat protozoan and retrovirus co-infections ##STR00001##