The invention relates to organic chemistry, in particular, to a novel crystal modification of 6-hydroxy-4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]-quinoline-5-carboxylic acid para-metoxyanilide with a diuretic effect, which can be used in the chemical-pharmaceutical industry and medicine. The objective of the present invention Is to prepare a novel crystal modification of 6-hydroxy-4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]-quinoline-5-carboxylic acid para-metoxyanilide with more advantageous pharmaceutical and biological properties. Said objective is achieved by the preparation of a novel crystal modification of 6-hydroxy-4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]-quinoline-5-carboxylic acid para-metoxyanilide (β-form) characterized by the following interplanar spacings (d) and relative intensities of the reflections (Irel) exhibiting an added enhanced diuretic effect.
