Spectra, calculated by Monte Carlo, are presented for neutrons transmitted through various thicknesses of iron from sources of fission neutrons, H2O-moderated fission neutrons, D2O-moderated fission neutrons, and 14.7-MeV neutrons. The sources were located at the center of iron spheres or were in the form of beams incident normally on slabs. Variations in spectral shapes are discussed from the viewpoint of effects on the response of neutron dosimeters. Effective cross sections for threshold detectors 103Rh, 115In, 32S, 237Np, 232Th, and 238U were obtained by averaging the cross sections over the calculated spectra. Average kerma , dose equivalent, and maximum dose per n/cm2 were also calculated. Curves of show the sensitivity of these detectors to spectral changes and permit the computation of correction factors to dosimeter readings.