  Surface brightness fluctuations (SBF) have been detected for three elliptical
galaxies-NGC 3379 in the Leo group, NGC 4406 in the Virgo cluster, and NGC 4373
in the Hydra-Centaurus supercluster-using marginally-sampled, deep images taken
with the Planetary Camera of the WFPC-2 instrument on the Hubble Space
Telescope (HST). The power spectrum of the fluctuations image is well-fit by an
empirical model of the point-spread function (PSF) constructed using point
sources identified in the field. The previous ground-based SBF measurements for
NGC 3379 and NGC 4406 are recovered, thereby demonstrating the capability of
the Planetary Camera of WFPC-2 to measure distances using the SBF technique
despite the marginal sampling of the images. The residual variance due to
unresolved sources in all three galaxies is only 2-5% of the detected
fluctuations signal, which confirms the advantage of HST imaging in minimizing
the uncertainty of this SBF correction. Extensive consistency checks, including
an independent SBF analysis using an alternate software package, suggest that
our internal uncertainties are < 0.02 mag. The fluctuations magnitude for NGC
4373 is I814bar = 31.31 +/- 0.05 mag, corresponding to a distance modulus of DM
= 32.99 +/- 0.11. This implies a peculiar velocity for this galaxy of 415 +/-
330 km/s, which is smaller than derived from the D_n-sigma relation. These
results demonstrate the power of the post-repair HST to measure distances to
elliptical galaxies at significant redshifts using the SBF technique.
