  In this talk, I present new results [1] obtained from QCD spectral sum rules
(QSSR), on the bag constant parameters entering in the analysis of the
B^0_{(s)}-\bar B^0_{(s)} mass-differences. Taking the average of the results
from the Laplace and moment sum rules, one obtains to order \alpha_s:
f_B\sqrt{\hat B_B}= (228 +- 61) MeV, f_{B_s}\sqrt{B_{B_s}}/{f_{B}\sqrt{B_{B}}=
1.18 +- 0.03, in units where f_\pi=130.7 MeV. Combined with the experimental
data on the mass-differences \Delta M_{d,s}, one obtains the constraint on the
CKM weak mixing angle: |V_{ts}/V_{td}|^2 > 20.2(1.3). Alternatively, using the
weak mixing angle from the analysis of the unitarity triangle and the data on
\Delta M_d, one predicts \Delta M_s=18.3(2.1) ps^{-1} in agreement with the
present experimental lower bound and within the reach of Tevatron 2.
