  Let A_i be a family of unital C*-algebras, respectively, of von Neumann
algebras and phi: N_0 \to C. We show that if a Hankel matrix related to phi is
trace-class, then there exists a unique completely bounded map M_phi on the
reduced free product of the A_i, which acts as an radial multiplier. Hereby we
generalize a result of Wysocza\'nski for Herz-Schur multipliers on reduced
group C*-algebras for free products of groups.
