  The characteristic double-bumped spectral energy distribution (SED) of
blazars is explained by either leptonic or hadronic models. In the former,
Inverse Compton emission dominates the emission of the high energy bump, while
proton synchrotron emission and proton-gamma interactions dominate it in the
latter. We present a new stationary lepto-hadronic code that evaluates both the
leptonic and the hadronic interactions. Apart from the modelling of the SED
produced in a leptonic or hadronic model, the code permits the study of
interesting mixed lepto-hadronic scenarios, where both processes contribute
significantly to the high energy bump. A first application to data from the
high frequency peaked BL Lac object PKS 2155-304 is discussed.
