  Preliminary results on pion-pion Bose-Einstein correlations in central Pb+Pb
collisions measured by the NA49 experiment are presented. Rapidity as well as
transverse momentum dependence of the HBT-radii are shown for collisions at 20,
30, 40, 80, and 158 AGeV beam energy. Including results from AGS and RHIC
experiments only a weak energy dependence of the radii is observed. Based on
hydrodynamical models parameters like lifetime and geometrical radius of the
source are derived from the dependence of the radii on transverse momentum.
