When q is an interpolating Blaschke product, we find necessary and sufficient conditions for a subalgebra B of H ∞ [ q ¯ ] to be a maximal subalgebra in terms of the nonanalytic points of the noninvertible interpolating Blaschke products in B . If the set M ( B ) ⋂ Z ( q ) is not open in Z ( q ) , we also find a condition that guarantees the existence of a factor q 0 of q in H ∞ such that B is maximal in H ∞ [ q ¯ ] . We also give conditions that show when two arbitrary Douglas algebras A and B , with A ⫅ B have property that A is maximal in B .