We present a simple formula for the total cross section sigma(nu N) of neutral- and charged-current deep-inelastic scattering of ultrahigh-energy neutrinos on isoscalar nuclear targets, which is proportional to the structure function F-2(nu N) (M-V(2)/s, M-V(2)), where M-V is the intermediate-boson mass and s is the square of the center-of-mass energy. The coefficient in front of F-2(nu N) (x, Q(2)) depends on the asymptotic low-x behavior of F-2(nu N). It contains an additional lns term if F-2(nu N) scales with a power of ln(1/x). Hence, an asymptotic low-x behavior F-2(nu N) proportional to ln(2)(1/x), which is frequently assumed in the literature, already leads to a violation of the Froissart bound on sigma(nu N).