From a sample of 146 900 hadronic Z0 decays recorded by the OPAL detec
tor at LEP, we have studied the azimuthal correlations of particles in
hadronic events. It is expected that these correlations are sensitive
to interference effects in QCD. We have compared the data to QCD Mont
e Carlo models which include and which do not include interference eff
ects. We find that the distributions of azimuthal correlations are not
reproduced by the parton shower models we have tested unless interfer
ence effects are included, no matter which hadronisation scheme is use
d.