It is usually assumed that the Flory-Huggins interaction parameter chi in polymer blends can be represented by a structureless, pointlike interaction. On a local scale, however, the Flory-Huggins parameter must show a spatial dependence as it basically reflects the segment-segment interaction potential. We show that SANS can be used to access this spatial dependence and that even in the SANS regime, a pronounced Q dependence of chi is found. The polymer blend used in the experiments was a polystyrene/poly(p-methylstyrene) blend. As we did not want to rely on literature values for the segment lengths of PS and PPMS, respectively, we measured the isotope blends of h-PS/d-PS and h-PPMS/dPPMS separately. A modified random phase formula based on the PRISM theory of Schweizer and Chandler is used to evaluate the data and fit a simple model to chi(Q). We find that the range of a Yukawa-like segment-segment interaction potential is about 9 Angstrom.