Two meso-tetra[(nido-carboranylmethyl)phenyl]porphyrins (para- and meta-regioisomers) and their corresponding Zn(II) complexes have been synthesized with the aim of studying the effect of carborane distribution and metalation on the biological properties of this series of compounds. In vitro cell toxicity, uptake/efflux, and subcellular localization using rat 9L, mouse B16 and/or human U-373MG cells were evaluated. All four amphiphilic porphyrins display very low cytotoxicities and time- and concentration-dependent uptake by cells, which is influenced by serum proteins. Preliminary subcellular localization studies suggest that one of these compounds localizes in close proximity to the cell nucleus. All four nido-carboranylporphyrins show promise as boron-carriers for the boron neutron capture therapy of cancers, particularly the metal-free nido-carboranylporphyrins 5 and 12, which are able to deliver higher amount of boron to cells in vitro than the corresponding zinc complexes.