  Using an approach to analyze the theta dependence of systems with a
theta-term we recently proposed, the critical behavior of CP^1 at theta=pi is
studied. We find a region outside the strong coupling regime where Haldane's
conjecture is verified. The critical line however does not belong to the
universality class of the Wess-Zumino-Novikov-Witten model at topological
coupling k=1 since it shows continuously varying critical exponents.
