Let G be a locally compact group and B(G) the Fourier-Stieltjes algebra of G. Pursuing our investigations of power bounded elements in B(G), we study the extension property for power bounded elements and discuss the structure of closed sets in the coset ring of G which appear as 1-sets of power bounded elements. We also show that L 1 -algebras of noncompact motion groups and of noncompact IN-groups with polynomial growth do not share the so-called power boundedness property. Finally, we give a characterization of power bounded elements in the reduced Fourier-Stieltjes algebra of a locally compact group containing an open subgroup which is amenable as a discrete group.Introduction. An element a of a Banach algebra A is said to be power bounded if sup n∈N a n < ∞. Power bounded elements in Banach algebras, especially power bounded operators on Banach spaces, have been studied by several authors, with emphasis on the impact on spectra [1], [23], [30], [31]. Power boundedness of measures on the real line has first been dealt with in [4] (see also [2] and [5] for related problems). For general locally compact abelian groups G, the most comprehensive work on power boundedness in the measure algebra M (G) and the L 1 -algebra L 1 (G) is due to Schreiber [34]. Actually, [34] has substantially influenced and inspired our previous investigations [20]-[22] on power boundedness in Fourier and Fourier-Stieltjes algebras of locally compact groups, and also the present study. Naturally, for nonabelian groups the proofs turn out to be much more involved.In [20, Theorem 4.1] we have shown that if G is an arbitrary locally compact group and u is any power bounded element of B(G), then the sets