We calculate neutrinoless double-..beta.. decay due to doubly charged Higgs bosons, which occur naturally in left-right-symmetric models. We find that the comparison with known half-lives yields values of phenomenological parameters which are compatible with earlier analyses of neutral-current data. In particular, we obtain a right-handed gauge-boson mass lower bound of the order of 240 GeV. Using this result and expressions for neutrino masses derived in a parity-nonconserving left-right-symmetric model, we obtain me-italic< or =1.5 eV, m..mu..< or =0.05 MeV, and mtau< or =18 MeV.