The recombination of excess electron-hole pairs in indium antimonide has been studied in the temperature range 200°K-15°K, where it is controlled by localized centers. Minority carrier trapping is found in extrinsic p-type material. The lifetimes of electrons and holes obtained from photoconductivity and photoelectromagnetic effect data on n- and p-type samples lead to a model for the recombination, consisting of a donor center having two energy levels in the forbidden gap, at 0.055 and 0.12 ev above the valence band. The capture coefficients for holes and electrons have been determined for the center in each of the two charge states. In p-type material, the chemical acceptors are in statistical equilibrium with the free holes in the valence band. When holes freeze out onto acceptor centers (T<60°K), an increase of free holes due to photoexcitation leads to a corresponding increase in the hole concentration on the acceptors. This effect of majority carrier trapping reduces the rise of hole lifetime with decreasing hole concentration. In order to determine the nature of the recombination centers, different treatments are used to introduce additional centers. It is found that bombardment with 4.5-Mev electrons produces additional centers having the same recombination properties as the original centers. The result indicates that the recombination centers have the nature of structural defects rather than chemical impurities. © 1961 The American Physical Society.