Possible experimental demonstration of the reduction hypothesis is dis
cussed. It is argued that the two-time distribution function w(t(1), t
(2),)measurable in the time-of-flight experiments, can not be calculat
ed without the reduction postulate. The calculation of w(t(1), t(2)),
using the Wigner rule and a model of the particle's detection process,
is presented. (C) 1998 Published by Elsevier Science B.V.