  We apply quantum field theory to study the excitation spectrum of doped
two-leg ladders. It follows from our analysis that throughout most of the phase
diagram the spectrum consists of degenerate quartets of kinks and anti-kinks
and a multiplet of vector particles split according to the symmetry of the
problem as 3 + 2 +1. This basic picture experiences corrections when one moves
through the phase diagram. In some regions the splitting may become very small
and in others it is so large that some multiplets are pushed in the continuum
and become unstable. At second order transition lines masses of certain
particles vanish. Very close to the first order transition line additional
generations of particles emerge. Strong interactions in some sectors may
generate additional bound states (like breathers) in the asymmetric charge
sector. We briefly describe the properties of various correlation functions in
different phases.
