Abstract: A method is disclosed for production of 1-alkyl-4(1H)-oxo-cinnolin-3-carboxylic acids. Mesoxalic acid dialkylester-3,4-methylenedioxy-phenylhydrazone is saponified using 1 to 1.5 Mol alkali into the corresponding monoalkylester, which is cyclicized with a Friedel-Crafts catalyst in the presence of a carboxylic acid anhydride into 6,7-methylenedioxy-4(1H)-oxo-cinnolin-3-carboxylic acid alkylester, which is alkylated with a C.sub.1 -C.sub.4 alkyl halogenide in the presence of alkali in a suitable solvent, after which the ester is saponified. Small amounts of byproduct alkylated in the 2-position are removed by brief heating and precipitation from alkaline solution, leaving a pure 1-alkyl product. The product is useful for the treatment of urinary tract infections.