The aim of this project is to set up a novel combined wide field, confocal laser-scanning and near-field microscope for fluorescence studies of biological systems. The setup will allow to monitor the distribution of proteins in biological samples by fluorescence microscopy and to identify and localize protein interactions by means of fluorescence resonance energy transfer. Both methods will benefit substantially from the complementary techniques of confocal laser-scanning microscopy (CLSM) and scanning near-field optical microscopy (SNOM). While CLSM allows to create almost arbitrary crossections from the fluorescence distribution in a specimen, SNOM is extremely sensitive to processes on the sample surface and allows to achieve a spatial resolution of below 100 nm. The feasibility of the setup for the study of protein distributions and protein-protein interactions will be demonstrated exemplarily in an investigation of the interaction mechanisms of the HIV-1 transactivator protein Tat.