Eight nitropyridinesulfonamides and pyridinesulfonamide N-oxides as their bioisosteres were prepared and evaluated for anticoccidial activity. Of these compounds, 2-, 4- and 5-nitropyridine-3-sulfonamides and pyridine-2- and -3-sulfonamide N-oxides were found to be active against Eimeria tenella. Thus, the relative positions, ortho or meta, of the substituents in nitropyridine-3-sulfonamides and pyridinesulfonamide N-oxides are important for anticoccidial activity. N-Substituted analogues of 5-nitropyridine-3-sulfonamide were also prepared and optimal anticoccidial activity was attained with the sulfonamide and its lower N-alkyl derivatives. The mode of action of 5-nitropyridine-3-sulfonamide was examined and found to be active in the sporozoite and the first schizogony stages.