We generalize a theorem of Bellow and Calder\'on concerning the a.e.
convergence of the convolution powers \ds \mu^nf(x)=\sum_{k}\mu^n(k)f(T^k x)
where T is a measure preserving transformation of a probability space and
μ is a probability measure on the integers.Comment: 13 pages, to appear in Annales de l Institut Fourie