An examination of the Brazilian newspaper O Combate, this article accomplishes four goals. First, it defines the politics of a periodical long cited but little understood by historians. Second, it documents O Combate's place, alongside other ‘yellow press’ outlets, in the making of a ‘public sphere’ in São Paulo. Third, it situates the same publications' role in the bringing into being of a more commercial, publicity-driven press, which would shed the yellow press's radicalism and abet the collapse of the public sphere of its heyday. Fourth, it suggests that O Combate's radical republicanism was one fount of the democratic radicalism of the late 1920s and early 1930s, as well as of the regionally chauvinist constitutionalism of 1932–7. In this rare application of the ‘public sphere’ idea to twentieth-century Brazil, readers may also detect an account closer to Jürgen Habermas’ original formulation than that found in the historiography of nineteenth-century Spanish America.