  We consider a free interpolation problem in Nevanlinna and Smirnov classes
and find a characterization of the corresponding interpolating sequences in
terms of the existence of harmonic majorants of certain functions. We also
consider the related problem of characterizing positive functions in the disc
having a harmonic majorant. An answer is given in terms of a dual relation
which involves positive measures in the disc with bounded Poisson balayage. We
deduce necessary and sufficient geometric conditions, both expressed in terms
of certain maximal functions.
