Three muoniated azacyclohexadienyl radical isomers were produced by the addition of muonium to pyridine in liquid pyridine and in high silica ZSM-5 zeolite (Si/Ai = 450) at 298 K, and observed with avoided level crossing muon spin resonance. The hyperfine coupling constants of the azacyclohexadienyl radicals are similar in both environments, which indicates that the radicals do not interact strongly with the zeolite framework. The relative yield of the three radicals depends on the medium, with the yield of the para isomer being six times larger in ZSM-5.