Zebrafish (Danio rerio) is a small tropical fish that has rapidly become an excellent model for biomedical studies. Zebrafish are inexpensive to maintain and breed readily. The young fish are small and relatively transparent which enables researchers to make microscopic observations in the living animal. This research project aims to develop an exciting new technology that will allow us to watch individual cells in the intact animal. To do this we will fluorescently label individual cells which will allow us to follow them using high-resolution microscopy. This new technology will also allow us to target specific molecules within these labelled cells to disrupt their activity. The molecules that we will target play important roles in regeneration, stem cells and cancer. After we disrupt the function of a molecule, we will be able to watch the cell to see whether its movement, division or differentiation potential are affected. For example we can test whether disruption of one molecule in a cell causes it to divide rapidly and form a tumour. This method will even allow us to follow what happens to an individual cell over a period of months or years. These exciting new tools will enable many researchers around the world to answer unresolved questions and will open up many new areas for biomedical research.