This is a review of methods for the solution of non-LTE radiative
transfer equations in long cylinders. The principal goal of these
methods is the modelling of elongated structures
imbedded in the solar corona, such as loops or prominence threads.
These objects are submitted to the solar radiation, which determines
the boundary conditions of the problem. Different cases are
examined. Concerning the geometry, one-dimension and two-dimension
cases are treated. The two-dimension case itself is subdivided into
(radius, altitude) and (radius, azimuth) problems, which are treated by
quite different methods. Another distinction concerns the method of
resolution: semi-analytical, Monte-Carlo and finite-difference
methods are examined. Some methods are restricted to a two-level
atom, others allow the treatment of realistic multilevel cases. Some
recent results, obtained with finite-difference, accelerated
Λ-iteration methods, are presented.