The interplanetary solar wind depletion (SWD) event of 26 April 1999 and its magnetospheric consequences are examined. The SWD event is characterized by a solar wind density decrease from ~3.0 to 0.7 cm-3 leading to a solar wind ram pressure decrease from ~2.0 to 0.2 nPa. This SWD onset is followed by a depolarization of nightside magnetospheric fields. At approximately the same time, an auroral pseudo-breakup occurred in the near-midnight auroral zone. A model is presented to explain the pseudobreakup as energy release by the tail magnetic field reconfiguration. The release of magnetic tension energy is estimated to have been ~3.3¿1019 ergs, while the auroral energy was approximately 30 % of this value, ~1.0¿1019 ergs. This result may imply that the magnetic field collapse led to direct particle acceleration through parallel electric fields. ¿ 2000 American Geophysical Union