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Zinc antimonides are interesting as thermoelectric materials, since their constituents are relatively cheap and abundant, and a number of compounds have exhibited good thermoelectric figures of merit. This paper focuses on theoretical studies of BaZn(2)Sb(2), CaZn(2)Sb(2), and ZnSb using density functional theory. In all compounds, a gap at the Fermi level is found which can be rationalized using the Zintl Klemm principle. On the basis of electronic structure calculations, the transport properties are calculated using Boltzmann transport theory. BaZn(2)Sb(2) as both p and n-type is found to have favorable properties along the b-axis. ZnSb was predicted to have favorable thermoelectric properties as n-type. Minima in the lowest conduction band in ZnSb are rationalized as stemming from increased bonding between distant neighbors at special k-points. By comparing the calculated transport properties to experimental measurements from literature, the carrier concentrations, band gaps, and relaxation times of the compounds are determined and the relevance of a constant kappa(l)/tau approximation is discussed.