Abstract.Let / be any fixed positive integer and a a sentence in the first-order predicate calculus of/unary functions. For positive integers n, an «-structure is a model with universe {0,1,...,« -1} and/unary functions, and p(n,a) is the ratio of the number of «-structures satisfying a to n"f, the number of «-structures. We show that lim"_00/i(«, a) exists for all such a, and its value is given by an expression consisting of integer constants and the operators +,-,,/, and ex.