Abstract. The role playing by the soft ( GeV/c) region in the small- behaviour of and the non-singlet structure function has been studied with the help of the effective QCD Lagrangian which takes into account the lightest degrees of freedom the constituent quarks and the -mesons (Goldstone bosons). It has been shown that the quark-quark interaction due to the pion exchange has a negative coupling for the isovector component ( in the -channel) of and isosinglet component of . Here the pion induced interaction changes mainly the normalization of the quark distribution (it decreases two times at ) and changes slightly the effective exponents ( , at ). On the other hand due to a positive value of coupling the value of increases by 15% for the isovector part of and up to (instead of without the pion contribution) for the isoscalar non-singlet structure function .