  We reexamine the scale dependence of twist-three correlation functions
relevant for the single transverse spin asymmetry in the framework of collinear
factorization. Evolution equations are derived for both the flavor-nonsinglet
and flavor--singlet distributions and arbitrary parton momenta. Our results do
not agree with the recent calculations of the evolution in the limit of
vanishing gluon momentum. Possible sources for this discrepancy are identified.
