  We discuss realizations of the SL(2,R) current algebra in the hyperbolic
basis using free scalar fields. It has been previously shown by Satoh how such
a realization can be used to describe the principal continuous representations
of SL(2,R). We extend this work by introducing another realization that
corresponds to the principal discrete representations of SL(2,R). We show that
in these realizations spectral flow can be interpreted as twisting of a free
scalar field. Finally, we discuss how these realizations can be obtained from
the BTZ Lagrangian.
