The InSpeck™ Green Microscopy Image Intensity Calibration Kit provides microsphere standards that generate a series of well-defined fluorescent intensity levels for constructing calibration curves and evaluating sample brightness. Each kit includes six separate suspensions of 2.5 μm fluorescent microspheres with relative fluorescence intensities of 100%, 30%, 10%, 3%, 1% and 0.3% covering the range of intensities commonly encountered in microscopy applications. Unstained control beads and mounting medium are also supplied. The aqueous suspensions of microspheres may be applied directly to the sample for calibrating fluorescence intensities or mounted separately in an adjacent well or on another slide.