This assay is an economical one step procedure for determining the effects of drugs or proteins on tubulin polymerization. It is an adaptation of an assay originally described by Bonne, D. et al. (1). Polymerization is followed by fluorescence enhancement due to the incorporation of a fluorescent reporter into microtubules as polymerization occurs. The standard assay uses neuronal tubulin (Cat. # T240), which generates a polymerization curve representing the three phases of microtubule formation; namely nucleation, growth and steady state equilibrium. Other tubulins, such as HeLa cell tubulin (Cat. # H001) can also be used in this assay. The low volume per assay of 50 µl and the low tubulin concentrations, 2 mg/ml final concentration (100 µg per assay), makes this an ideal choice for studying the more expensive cancer cell tubulin reagents and for high throughput applications.