The phenomenon of swelling of several long polymer chains (length N), mixed at concentrations below c* in a series of shorter chain "solvents" (length P), has been quantitatively studied by small-angle neutron scattering. The blends consist of perdeuterated polystyrene guest chains (M-w = 87 000-2 950 000), in hydrogenous PS hosts (M-w = 2 530-2 000 000). Scaling relationships have been established for the long chain’s radius of gyration R-g and second virial coefficient A(2). For bimodal blends where the long chain is in the unswollen regime (P > N-1/2), the scaling is that of a random walk chain, with R-g similar to N0.504+/-0.009 and A(2) similar to P-0.95+/-0.24. For the swollen regime, one observes R-g similar to N0.59+/-0.02P-0.10+/-0.02 and A(2) similar to N-1/5P-0.59+/-0.10. The weaker than predicted dependence of R-g on P, -1/10 vs -1/5 from theory, implies that in the swollen regime, the screening blob size xi depends on P-1/2 rather than P as originally hypothesized. The approximate crossover point at qR(g)(short) approximate to 1 in the static structure factor of the long chain from S(q) similar to q(-1.7) for large distances (excluded volume) to ideal chain statistics S(q) similar to q(-2) at smaller scales is seen as a confirmation of the screening effect of the short chains.