Infrared reflectance and Faraday rotation data were obtained for pure and for highly Al‐dopedn‐type ZnSe crystals. Comparison of these data gave the free‐carrier contribution to the dielectric constant and Faraday rotation, which, in turn, yielded the electron effective mass and carrier concentration. The result for the effective mass ratio,m*/m=0.17±0.025, agrees satisfactorily with previous estimates. The Hall scattering constantrwas obtained from the optically measured carrier concentration and Hall effect data on the optical samples. The result,r≃1.4, forN≃0.7Ndeg, is consistent with values found in other II‐VI compounds.