Measurements of the two-photon absorption coefficient in semiconductor-doped glasses were performed. The imaginary part of the third-order optical susceptibility in the semiconductor particles is derived by combining nonlinear-optical-transmission data with small-angle neutron-scattering (SANS) results, which give the volume fraction of the nanocrystals. We find that the absorptive nonlinearity of the nanocrystals (with radii, also measured by SANS, in the range 2\char21{}11 nm) is close to that of the bulk semiconductor, in contrast to recent predictions and data.