  We show that O(2,2) transformation of SU(2) WZNW model gives rise to marginal
deformation of this model by the operator $\int d^2 z J(z)\bar J(\bar z)$ where
$J$, $\bar J$ are U(1) currents in the Cartan subalgebra. Generalization of
this result to other WZNW theories is discussed. We also consider O(3,3)
transformation of the product of an SU(2) WZNW model and a gauged SU(2) WZNW
model. The three parameter set of models obtained after the transformation is
shown to be the result of first deforming the product of two SU(2) WZNW
theories by marginal operators of the form $\sum_{i,j=1}^2 C_{ij} J_i \bar
J_j$, and then gauging an appropriate U(1) subgroup of the theory. Our analysis
leads to a general conjecture that O(d,d) transformation of any WZNW model
corresponds to marginal deformation of the WZNW theory by combination of
appropriate left and right moving currents belonging to the Cartan subalgebra;
and O(d,d) transformation of a gauged WZNW model can be identified to the
gauged version of such marginally deformed WZNW models.
