Vacuum Instability and Higgs Scalar Mass

A procedure is given to estimate the decay probability of a metastable vacuum state in quantum field theory. As an application, in the Weinberg-Salam model the lower bound (for ${\theta }_{\mathrm{W}}=35\mathrm{}°$) on the Higgs mass can be reduced from 4.9 GeV, corresponding to effective stability of a metastable vacuum.