Tubulin, the structural subunit of microtubules, is the target of some highly successful anti-tumor drugs. Most of these drugs bind to the beta-tubulin resulting in the inhibition of microtubule dynamics and eventually cell death. The varied cellular distribution of several human isotypes of beta -tubulin provides a platform upon which to construct novel chemotherapeutic agents that are able to differentiate between these types of cells. To test this hypothesis, we have previously created homology models of the nine most frequently observed human beta -tubulin isotypes and analyzed them for differences in the colchicine-binding site. Here, we describe the electrostatic properties of the colchicine binding site and how this may affect calculated drug binding affinities between the beta -tubulin isotypes.