The reaction of 5-hydroxy-1-pyrrolines with arenes in TfOH at room temperature for 1 h afford 5-aryl-1-pyrrolines in 55–98 % yields. 5-Hydroxy-1-pyrrolines in TfOH or H₂SO₄ at room temperature for 0.5–1 h undergo dehydration with the formation of N-protonated forms of 3H-pyrroles, which were characterized by NMR. Upon hydrolysis, the N-protonated species give quantitatively the corresponding 3H-pyrroles. The intermediate cationic species derived from the protonation of 5-hydroxy-1-pyrrolines in Brønsted acids have been studied by means of NMR and DFT calculations. Plausible reaction mechanisms are discussed.