We present total internal reflection fluorescence microscopy (TIRFM) measurements of colloidal CdSe quantum dots (QDs). This technique provides the advantage of recording the time-resolved fluorescent signal of many single QDs simultaneously, thus allowing data with high statistical confidence to be obtained in a relatively short time. We discuss methods of taking and extracting the data from the collected images, and in particular, investigate the on/off intermittent fluorescence behavior from single QDs over a range of excitation intensities.We find that on/off-times are independent of the excitation power at intensities above 0.2 kW/cm2, while at lower intensities, there is a pronounced dependence. We discuss the observed behavior in terms of current physical models of QD ionization and neutralization, which are often used to explain the on and off blinking.