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We present a simple, effective approach for estimating the on-orderbackgrounds of spectra taken with the highest-resolution modes of the SpaceTelescope Imaging Spectrograph (STIS) on-board the Hubble Space Telescope. Ourscheme for determining the on-order background spectrum uses polynomial fits tothe inter-order scattered light visible in the two-dimensional STIS MAMAimages. We present a suite of high-resolution STIS spectra to demonstrate thatour background subtraction routine produces the correct overall zero point, asjudged by the small residual flux levels in the centers of strongly-saturatedinterstellar absorption lines. Although there are multiple sources ofbackground light in STIS echelle mode data, this simple approach works verywell for wavelengths longward of Lyman-alpha. At shorter wavelengths, thesmaller order separation and generally lower signal-to-noise ratios of the datacan reduce the effectiveness of our background estimation procedure. Slightartifacts in the background-subtracted spectrum can be seen in some cases,particularly at wavelengths <1300 Ang. Most of these are caused by echellescattering of strong spectral features into the inter-order light. We discussthe limitations of high-resolution STIS data in light of the uncertaintiesassociated with our background subtraction procedure. We compare ourbackground-subtracted STIS spectra with GHRS Ech-A observations of the DA whitedwarf G191-B2B and GHRS first-order G160M observations of the early-type starHD 218915. We find no significant differences between the GHRS data and theSTIS data reduced with our method in either case.

Background and Scattered-Light Subtraction in the High-Resolution Echelle Modes of the Space Telescope Imaging Spectrograph