4-(2,7-Dimethyl-4-oxo-1,3-thiazolo[4,5-<i>d</i>]pyridazin-5-yl)benzenesulfonamide

The thia-zole-pyridazine fused-ring system of the title compound, C(13)H(12)N(4)O(3)S(2), is approximately planar (r.m.s. deviation = 0.037 Å); the benzene ring connected to the fused-ring system through the N atom is twisted by 39.3 (1)°. The amine group uses an H atom to form a hydrogen bond to the ketonic O atom of an inversion-related mol-ecule to generate a dimer; adjacent dimers are linked by an N-H⋯O hydrogen bond to form a linear chain.