Soft X-ray observations of a filament located near NOAA AR 4640 were obtained with the Flat Crystal Spectrometer (FCS) on board the Solar Maximum Mission satellite over the nine day period 3-12 April 1985. On 7 April the filament partially lifted off. At the same time and location an enhancement was imaged in soft X-rays. A total of 16 hours of FCS observations, including 25 raster images, were made of the filament prior to the eruption, and over 40 hours of observations, including 57 raster images, were made following the eruption. Careful alignment of Hα images taken during the same period has made possible the calculation of the integrated soft X-ray emission around the filament channel before, during, and after the eruption. Kìtt Peak magnetograms have also been examined for this period to determine the corresponding magnetic field structure. A time history of the eruption in X-ray and optical wavelengths, and the development of the magnetic field structure are presented. Evidence is seen for X-ray brightening in pre-existing magnetic field loops over the filament.