Abstract: The invention relates to novel 3(2H)-pyridazinone-derivatives of the general formula (I), pharmaceutical compositions containing them and process for their preparation. In the general formula (I) ##STR1## stands for an ethyl or propyl group substituted by a terminal halogen atom or a hydroxyl or NR.sup.1 R.sup.2 group, whereinR.sup.1 represents hydrogen atom or an unsubstituted or optionally substituted benzyl group;R.sup.2 represents hydrogen atom or an unsubstituted or optionally substituted benzo[1,4]dioxan-2-yl-methyl or -ethyl group or a (CH.sub.2).sub.n --R.sup.3 group, whereinn is 2 or 3; andR.sup.3 stands for an unsubstituted or optionally substituted phenoxy or phenylthio group; andX stands for a hydrogen or halogen atom or an unsubstituted or optionally substituted, saturated or unsaturated 5- or 6-membered heterocyclic group containing a nitrogen atom and optionally an additional heteroatom, e.g.

Abstract: The invention relates to novel pyrimido [5,4-b][1,4]oxazine derivatives of the formula (I), and the acid addition salts thereof, pharmaceutical compositions containing them and a process for their preparation. In the formula (I) ##STR1## wherein R.sup.1 stands for a C.sub.1-4 alkyl group;R.sup.2 stands for hydrogen or halogen or an azido group or an --NR.sup.5 R.sup.6 group, whereinR.sup.5 represents hydrogen or a benzyl group, or a C.sub.1-4 alkyl group unsubstituted or substituted by a hydroxyl group,R.sup.6 stands for hydrogen, an amino group, a C.sub.3-6 cycloalkyl group, a straight or branched-chain C.sub.1-4 alkyl group optionally substituted by a hydroxyl, mercapto, aminocarbonyl, furyl, 2-benzo[1,4]dioxanyl, di(C.sub.1-4 alkyl)amino group or by a phenyl or phenoxy group optionally mono- or polysubstituted by halogen or C.sub.1-4 alkoxy group (s) or by a 6-membered, saturated nitrogen-containing heterocycle optionally containing an additional nitrogen or oxygen atom and optionally substituted by a C.