The dynamics of molecular chains of hydrogen-bonded p-nitroaniline (pNA), confined in the one-dimensional pore system of AlPO4-5, was studied by broadband dielectric spectroscopy (10(-2)-10(6) Hz). Two relaxation processes were observed. A fast process (the alpha process) shows above 72 degrees C a Vogel-Fulcher-Tammann behavior typical of glass-forming materials, indicating cooperative dynamics of the "condensed" pNA chains. Below the glass temperature the alpha-relaxation peak broadens significantly and obeys an Arrhenius law. Both observations imply a change in length scale of cooperativity xi from a temperature-controlled to a chain-length-dependent one. The second relaxation process is tentatively assigned to structural relaxations of the AlPO4-5 host lattice itself, since it is also present in calcined (empty) crystals.