The boundary functions ϕ j of the Dirichlet problem, on the faces Γ j, j = 1, 2, ..., 6 of the parallelepiped R are supposed to have seventh derivatives satisfying the Hölder condition and on the edges their second, fourth and sixth order derivatives satisfy the compatibility conditions which result from the Laplace equation. For the error uh−u of the approximate solution uh at each grid point (x1, x2, x3), a pointwise estmation O(ρh6) is obtained, where ρ = ρ(x1, x2, x3) is the distance from the current grid point to the boundary of R; h is the grid step. The solution of difference problems constructed for the approximate values of the first and pure second derivatives converge with orders O(h6 |ln h|) and O(h5+λ), 0 < λ < 1, respectivly.