Abstract: Novel 8-alkylpyrido[3,4-d]pyridazines of the formula: ##STR1## wherein R.sup.1 stands for a lower alkyl group; R.sup.2 stands for a cyclic amino group, or pharmaceutically acceptable salts thereof, have excellent diuretic activity in mammals including human beings, so that they are useful for therapy for human or animal use.

Abstract: Novel 7-(hydroxyphenyl)pyrido(3,4-d)pyridazines of the formula: ##STR1## wherein R.sup.1 stands for hydrogen or a lower alkyl group; R.sup.2 stands for a cyclic amino group, or a pharmaceutically acceptable salt thereof, have excellent diuretic activity in mammals including human beings, so that they are useful for therapy for human or animal use.

Abstract: Pyrido (3,4-d) pyridazine derivatives are provided herein of the formula: ##STR1## wherein R.sub.1 is hydrogen or an alkyl group of 1 to 4 carbon atoms; R.sub.2 is a substituted or unsubstituted phenyl, naphthyl, furyl or pyridyl, the number of the substituents being one of two, the substituents being those selected from the group consisting of lower alkoxy groups of 1 to 3 carbon atoms, lower alkyl groups of 1 to 3 carbon atoms, halogens and nitros; R.sub.3 is hydrogen or a lower alkoxy group of 1 to 4 carbon atoms; and R.sub.4 is a substituted or unsubstituted morpholino, piperidino or pyrrolidino, the substituents being one or two, the substituents being those selected from the group consisting of methyl and ethyl groups, and at least one of the residue R.sub.2 and the residue R.sub.4 is substituted by one or two substituents, and a pharmaceutically acceptable salt thereof. The compounds of the present disclosure have effective and strong diuretic action and exhibit low toxicity characteristics.

Abstract: A pyrido [3,4-d] pyridazine derivative is provided herein of the formula: ##SPC1##Wherein R.sub.1 is hydrogen or an alkyl group of 1 to 4 carbon atoms; R.sub.2 is an alkyl group of 1 to 4 carbon atoms, an aralkyl group of 7 to 8 carbon atoms, or a substituted or unsubstituted phenyl, naphthyl, furyl or pyridyl, the substituent being a lower alkoxy group of 1 to 3 carbon atoms, a lower alkyl group of 1 to 3 carbon atoms, halogen or nitro; R.sub.3 is hydrogen or a lower alkoxy group of 1 to 4 carbon atoms; and R.sub.4 is a substituted or unsubstituted morpholino, piperidino or pyrrolidino, the substituent being methyl or ethyl and a pharmaceutically acceptable salt thereof. The compounds of the present invention have effective and strong diuretic action and exhibit extremely low toxicity characteristics.