Muon spin rotation (μSR) measurements of the internal magnetic fields in YBa2Cu3O7-δ are reported. Pronounced differences between field-cooled (FC) and zero-field-cooled (ZFC) μSR signals, hysteresis effects and flux trapping are observed. The μSR depolarization rate provides information regarding the local magnetic field distribution in the superconducting state. The present results show similarities to calculations that model a glasslike superconducting state. © 1988.