Given f (x, y) ∈ Z[x, y] with no common components with x a − y b and x a y b − 1, we prove that for p sufficiently large, with C( f ) exceptions, the solutions (x, y) ∈ F p × F p of f (x, y) = 0 satisfy ord(x) + ord(y) > c(log p/ log log p) 1/2 , where c is a constant and ord(r) is the order of r in the multiplicative group F * p . Moreover, for most p < N, N being a large number, we prove that, with C( f ) exceptions, ord(x) + ord(y) > p 1/4+ (p) , where (p) is an arbitrary function tending to 0 when p goes to ∞.