  The discovery of hard X-rays from tops of flaring loops by the HXT of YOHKOH
represents a significant progress in the understanding of solar flares. This
report describes the properties of 20 limb flares observed by YOHKOH from
October 1991 to August 1998, 15 of which show detectable impulsive looptop
emission. Considering the finite dynamic range (about a decade) of the
detection it can be concluded that looptop emission is a common feature of all
flares. The light curves and images of a representative flare are presented and
the statistical properties of the footpoint and looptop fluxes and spectral
indexes are summarized. The importance of these observations, and those
expected from RHESSI with its superior angular, spectral and temporal
resolution, in constraining the acceleration models and parameters is
discussed. briefly.
