  We discuss the precise relation of the open N=2 string to a self-dual
Yang-Mills (SDYM) system in 2+2 dimensions. In particular, we review the
description of the string target space action in terms of SDYM in a ``picture
hyperspace'' parametrised by the standard vectorial R^{2,2} coordinate together
with a commuting spinor of SO(2,2). The component form contains an infinite
tower of prepotentials coupled to the one representing the SDYM degree of
freedom. The truncation to five fields yields a novel one-loop exact lagrangean
field theory.
