  Given an interpolating Blaschke product $B$ with zeros $\{a_j\}$, we seek to
characterize the sequences of values $\{w_j\}$ for which the interpolation
problem $$f(a_j)=w_j\qquad (j=1,2,\dots)$$ can be solved with a function $f$
from the model subspace $H^1\cap B\overline{H^1_0}$ of the Hardy space $H^1$.
