  Isospin analysis has been used to constrain the CP-asymmetries in B -> pi pi
decays. In particular correlation between a weak phase \theta and a strong
phase \delta is obtained. Further using the experimental values for the
CP-average branching ratios, the following bounds on direct CP-asymmetries are
obtained: -0.35+/- 0.22=< C_{\pi ^+\pi^-}\leq 0; C_{\pi ^0\pi ^0}=-(2.4\pm 1.0)
C_{\pi ^+\pi ^-}. Constraints on mixing induced CP-asymmetries are also
discussed.
