The Leica Fluo LED 4000 and Fluo LED100 LED illumination systems offer very high image quality for fluorescence applications while being maintenance-free, compact and easy to operate. In addition to its flexibility for fluorescence applications in cell biology and neurobiology and for use in imaging facilities, the LED 4000 offers five precentered LED modules, that can be freely combined for multi-color experiments with different wavelengths. The compact illumination unit is directly connected to the microscope. If an additional wavelength is required, individual LED modules can easily be exchanged. For applications requiring one fluorochrome only, the Fluo LED 100 is a solution. In pathology, cytology, microbiology and immunohistochemistry, where usually only fluorescein is used, this ultra compact and user-friendly LED illumination with its excitation wavelength of 470 nm is suited.