Cells are typically visible under bright field optics without staining, especially if phase contrast optics are available. However, staining makes cells easier to see, and can reveal physiological states that bright field optics cannot. The Oris Assays impose no restrictions on choice of stain, and you can use multiple stains simultaneously if desired. To quantify migration/invasion via area closure, we recommend a fluorescent cytoplasmic stain such as TRITC-phalloidin in order to maximize signals for your detector. To quantify migration/invasion by counting cells, we recommend a nuclear stain such as DAPI. Restricting the stain to the nuclei creates smaller objects for imaging than do cytoplasmic stains, providing greater separation between individual cells and therefore more accurate counts. You may also consider pre-labelling cells prior to seeding in the Oris assays. However, some stains may impact migration and/or invasion, potentially creating experimental artifacts.