  The Synchrotron Proton Blazar model is a promising model to explain high
energy emission from gamma-ray loud BL Lac objects like Mkn 421. In contrast to
leptonic models, the hadronic explanation of gamma-ray emission predicts
ultrahigh energy neutrinos.
  The predicted neutrino spectra from a typical High-energy cutoff BL Lac
Object (HBL) and a Low-energy cutoff BL Lac Object (LBL) are presented. We find
that cooling due to muon synchrotron radiation causes a cutoff of the neutrino
spectrum at $\sim 10^{18}$ eV, with the exception of $\nu_\mu$ from kaon decay
which may extend to higher energies if meson production takes place in the
secondary resonance region of the cross section.
  The impact of the neutrino output from both source populations to the diffuse
neutrino background is discussed.
