The development of photactivatable (PA) variants of Green fluorescent protein (GFP) has allowed the dynamics of spatially restricted protein pools within living cells to be determined. Over the last 5 years, experiments utilizing PA-GFP fused to α-tubulin have provided important insights into the mechanisms that control microtubule dynamics in living cells. In this chapter, we describe the methodology required to generate stable cell lines expressing photoactivatable-GFP-α-tubulin and to derive quantitative measurements of tubulin turnover at microtubules plus-ends in living cells.