On the behaviour of non-singlet structure functions at small x

The resummation of O(alpha(s)(l+1) ln(2l) x) terms in the evolution kernels of non-singlet combinations of unpolarized and polarized structure functions is investigated. The agreement with complete calculations up to order alpha(s)(2) is demonstrated, and the leading small-x contributions to the three-loop non-singlet splitting functions P-+/- are derived. The additional contributions due to the resummed terms are studied numerically for the most important non-singlet structure functions. They are found to be about 1% or smaller in the kinematical regions accessible at present and in the foreseeable future.