We describe two types of molecular nitrogen fluorescence lidars which can be used to determine excited or ionized nitrogen density in the ionosphere during moderate or strong aurora. The lidars excite nitrogen already excited or ionized through impact with high-energy auroral electrons. Several different configurations are considered for both types of lidar. The first type of lidar is a conventional fluorescence lidar which operates in the first positive system (N2(A3∑+u)→N2(B3∏g)) or the first negative system (N+2(X2∑+g)→N+2(B2∑+u)). Several different lasers are considered. The choice of laser determines the bands for excitation and fluorescence. The second type of lidar first pumps excited N2 to a higher energy state and then does conventional fluorescence lidar on that state. This lidar utilizes two lasers. The first laser, the pump, operates in the first positive system. The second laser, the probe, operates in the second positive system (N2(B3∏g)→N2(C3∏u)). Both lidars are described in detail and results of signal to noise calculations are performed using reasonable system parameters. ¿ American Geophysical Union 1995