Differential absorption lidar (DIAL) and rotational Raman lidar allow measurements of tropospheric water vapor and temperature, respectively, with very high resolution. So far, these techniques have not yet been combined. In this contribution we present the concept for a lidar system, which employs these two techniques simultaneously and discuss synergetic effects. The combination allows relative humidity profiling with unprecedented resolution and accuracy. In addition, temperature, particle extinction coefficient, and particle backscatter coefficient data measured with rotational Raman lidar can be used to correct the water vapor DIAL data. These corrections are required when gradients in the backscatter ratio exist. We propose to transmit three laser wavelengths and to employ 6 receiver channels. Two infrared wavelengths are transmitted for the water vapor DIAL measurements and one ultraviolet wavelength for the rotational Raman measurements. 3 receiver channels detect the elastic backscatter signals, two channels are used for the detection of the ultraviolet rotational Raman backscatter signals with different temperature-dependency, and one channel is for a temperature-independent rotational Raman backscatter signal which is excited by the off-line infrared laser wavelength.