Results on the pion phase-space density at freeze-out in sulphur-nucleus, P
b-Pb and pi-p collisions at the CERN SPS are presented. All heavy-ion react
ions are consistent with the thermal Bose-Einstein distribution f = [exp(E/
T) - 1](-1) at T similar to 120 MeV, modified for radial expansion. pi-p da
ta are also consistent with f, but at T similar to 180 MeV and without radi
al flow.