  We study the effects of optically thick clumps, non-void inter-clump medium,
variation of the onset of clumping, and velocity dispersion inside clumps on
the formation of resonance lines. For this purpose we developed a full 3-D
Monte Carlo Radiative Transfer (MCRT) code that is able to handle 3-D shapes of
clumps and arbitrary 3-D velocity fields. The method we developed allows us to
take into account contributions from density and velocity wind inhomogeneities
to the total opacity very precisely. The first comparison with observation
shows that 3-D density and velocity wind inhomogeneities have a very strong
influence on the resonance line formation, and that they have to be accounted
for in order to obtain reliable mass-loss rate determinations.
