Abstract: This invention relates to a novel 1,8 benzo[b]naphythyridine derivative of general formula (I), ##STR1## wherein R is H or a hydroxy, amino or alkylamino radical optionally substituted by amino or hydroxy, or R is dialkylamino of which the alkyl portions may form, with the nitrogen atom, a 5- or 6-membered heterocyclic ring which optionally contains a further heteroatom chosen from nitrogen, oxygen or sulphur, or R is C.sub.3-6 cycloalkylamino or an alkanylamino, N-alkyl N-alkanylamino or aminoalkylphenylamino radical; R.sub.1 and R.sub.2, which are the same or different, are in positions 2 and 3 and represent H, alkyl, C.sub.2-4 alkenyl, phenyl, or substituted phenyl, or R.sub.1 and R.sub.2 are in position 2 and represent alkyl; R.sub.3 is H or alkyl, fluoroalkyl, carboxyalkyl, C.sub.3-6 cycloalkyl, fluorophenyl, difluorophenyl, alkyloxy or alkylamino; and R.sub.4 is H or F, wherein the C.sub.