A magnetospheric substorm that occurred at Sanae, Antarctica, on July 27, 1979, was observed by a variety of techniques. A synthesis of the observations is presented, and an attempt made to deduce details of the behavior of the magnetosphere-ionosphere system during the event. While there was some evidence of a growth phase, it was inconclusive. At the onset there was a rapid change in the tail field, which assumed a more dipolar form, accompanied by Pi 2 oscillations and the precipitation of 6-keV electrons, with brightening of the auroral arc, auroral-type sporadic E ionization, and riometer absorption. A positive spike was observed in the D magnetic component, instead of the expected negative one. There was no evidence of the usual westward traveling surge at the beginning of the expansion phase during which the precipitation region, auroral arc, and electrojet moved rapidly poleward, though it may have occurred outside the field of view from Sanae. The H&bgr; emission increased by a factor of less than 2, whereas the oxygen and nitrogen emissions monitored increased by 3--4. During the recovery phase, phenomena were consistent with a return of the tail field to an elongated form; a very high ratio of 557.7-nm' 630-nm emissions, exceeding 10, was observed; and the electrojet lagged noticeably behind the photon emission regions. ¿American Geophysical Union 1987