The magnetic responses of vacuum annealed polycrystalline Pb2Sr2PrCu3O8 to a magnetic field have been studied by ac magnetic susceptibility measurements, where both the in-phase component chi' and the out-of-phase component chi'' were measured. Diamagnetic responses in chi'(T) below 60 K were clearly seen, showing the occurrence of superconductivity, but it is filamentary. This filamentary superconductivity was also evident in the chi''(T). Under an applied de field, both the chi'(T) and chi''(T) behave as what are expected for a superconducting system. At lower temperatures, a well-defined peak associated with the Pr spin ordering is also clearly revealed at 5 K. Correspondingly, an anomaly is also seen in the specific heat data. (C) 1998 American Institute of Physics.