The electronic structure of Fe and Mn impurities and Ga and Sb vacancies in gallium antimonide has been investigated by the spin-polarized LMTO-TB method. Magnetic moments and total energies of doped zinc-blende crystals have been calculated making use of the 128-site supercells. Both anion and cation doping has been considered. For all types of doping Fe and Mn atoms stay magnetic with well localized magnetic moments, which are substantially less than their ionic values. Fe magnetic moment is 2.28μ B when at the cation site and 1.30μ B when at the anion site. Mn magnetic moments are 3.60μ B and 3.12μ B for the cation and anion sites, respectively. The total energies for supercells with and without magnetic impurities were used to determine the most probable sites for doping Fe and Mn atoms. Both magnetic atoms have larger binding energies when entering cation sites of the lattice. The position of magnetic electron levels relative to valence and conduction bands shows that Fe and Mn can provide both hole carriers and localized magnetic moments resulting in interesting combination of semiconducting and magnetic behavior. Possible lattice relaxation effects near impurity atoms are considered. The calculation results are compared with experimental data available for III-V systems.