  We examine long-wavelength correlation functions of massive scalar fields in
de Sitter spacetime. For the theory with a quartic self-interaction, the
two-point function is calculated up to two loops. Comparing our results with
the Hartree-Fock approximation and with the stochastic approach shows that the
former resums only the cactus type diagrams, whereas the latter contains the
sunset diagram as well and produces the correct result. We also demonstrate
that the long-wavelength expectation value of the commutator of two fields is
equal to zero both for spacelike and timelike separated points.
