The only known way to obtain indirect experimental information on the space-time structure of the particle emitting source created in relativistic heavy-ion collisions is two-particle (Hanbury-Brown- Twiss (HBT)) correlations. In particular a strong correlation between the momenta of the particles and the space-time emission point indicate expanding sources as predicted by hydrodynamical models. Calculations suggest that the contribution of the various resonances that decay after freezeout is mainly seen as a reduction of the correlation strength lambda at small K/sub T/ and distortion of the Gaussian shape for HBT spectra. (10 refs)