  As a first step towards the complete calculation of deep-inelastic scattering
at third order of massless perturbative QCD, we have computed the fermionic
(nf) contributions to the flavour non-singlet structure functions in
unpolarized electromagnetic scattering. We briefly discuss the approach chosen
for this calculation, the problems we encountered and the status of the
project. We show the results for the corresponding anomalous dimension in both
Mellin-N and Bjorken-x. Together with the nf part of A_3, our calculation
facilitates the complete determination of the threshold-resummation
coefficients B_2 and D_2^DIS. The latter quantity vanishes in the MSbar scheme.
