[en] The gradient-invariant theory of four-fermion weak interaction in the Blokhintsev stochastic space is constructed. Perturbation theory series and the conditions for gradient invariance in the stochastic theory are investigated. Specific processes are calculated and limits for ''the stochastic elementary length'' L(>=)10^-16 cm are obtained. The problem of neutrino oscillation is considered and the μ→eγ, μ→3e, Ksub(L)sup(0)→μe and K→πeμ decays are calculated within it's framework. It is shown that if L approximately 10^-16 cm and if mixing of neutrinos takes place, then the probability for these decays is close to the experimental one