A large geomagnetic storm began on September 4, 1984 with a storm sudden commencement (SSC) reported at 07:46 UT. Observations acquired with the AMPTE/CCE Magnetic Field Experiment have been used to determine the overall magnetic field environment during the evolution of the storm. The CCE spaccraft had reached apogee at 06:05 UT on that day and was moving slowly inward in the afternoon sector. At approximately 06:33 UT, when the spacecraft was at a 8.8 Re geocentric radial direction, an about 30% increase in total field was observed that is interpreted as a sudden impulse. The magnetic field observed by the CCE remained relatively stable and northward until 07:45 UT, when it began to fluctuate over a wide range of frequencies up to the 50 Hz limit of the instrument. Six magnetopause crossings were observed; four of them were separated by approximately 20 to 25 minutes. Magnetopause normals were estimated at all six crossings and were found to be approximately constant in direction, suggesting that the entire magnetosphere was ''breathing'' in and out with a period of about 45 minutes. The magnetic field variations stopped abruptly at approximately 10:00 UT when the CCE was at a 7.5 Re radial distance, where magnetosheath fields were observed, indicating that the magnetopause was displaced inward to at least this distance. A comparison of observed and theoretical magnetic fields for a series of CCE passes near perigee revealed the development of a significant and asymmetric ring current during the period following the SSC. The local time distribution of Dst as well as the in situ particle measurements confirm at least two separate developments of ring current disturbances at dusk without azimuthal symmetry until well after the storm recovery.