be a hypercube in n . We prove theorems concerning mean-values of harmonic and polyharmonic functions on () n I r , which can be considered as natural analogues of the famous Gauss surface and volume mean-value formulas for harmonic functions on the ball in n and their extensions for polyharmonic functions. We also discuss an application of these formulas-the problem of best canonical one-sided L 1-approximation by harmonic functions on