1. Introduction. For a prime p we denote by F p the finite field of p elements, which we assume to be represented by the set {0, 1, . . . , p − 1}. For an integer t we denote by Z t the residue ring modulo t and by Z * t the group of units of Z t .Let ϑ ∈ F * p be of multiplicative order t ≥ 1. There is a rather long history of studying the exponential sums with the powers ϑ n , n = M +1, . . . , M +N , where N ≤ t, in finite fields and residue rings: see [6,7,17,[21][22][23][26][27][28] for several results in this direction together with their numerous applications.Here we consider a presumably harder question about exponential sums with the roots ϑ 1/n , for n = M + 1, . . . , M + N with gcd(n, t) = 1 instead of the powers. More precisely, for an integer m > 0, we put