The precise localization of newly discovered proteins and messenger RNA molecules within cells is of crucial importance for assigning functions and testing mechanistic hypotheses. Such molecules can be visualized by fluorescent and electron-dense tags using standard techniques, and then need to be imaged in relation to surrounding structure by microscopy for localization. The confocal microscope provides the most effective means to do this by light microscopy, allowing complete three dimensional reconstructions with unprecedented detail. This instrument will serve the entire biological community at Princeton, whose research requires localizations of importance and molecular biology. At lest 80% of the 25 faculty in life sciences at Princeton will be user of both instruments, about 45% being major users.