We examine two factors that could limit the doping of n-type III-V semiconductor nanowires, namely, the solubility of the dopants and the possible formation of DX-like defect centers. We find that it is preferable to dope zinc-blende nanowires via anion substitution as opposed to cation substitution. The comparison with previous work on n-type III-V semiconductor nanocrystals also allows us to determine the role of dimensionality and quantum confinement on doping characteristics of materials. Our work is based on quantum calculations of InP nanowires using real-space pseudopotentials constructed within density functional theory.