We present high spectral and time resolution observations of high signal-to-noise ratio (above 200) of the beta Cephei star alpha Lupi, carried out for three different wavelengths during three nights. The radial velocity curves show a nice sinusoidal behaviour for all elements. However, the amplitude and the average velocity of the variation depend on the considered lines. By means of a simple least squares fit conducted on each observed night, we also point out a non-constancy of the pulsation period. A comparison between the RI and FWHM curves seems to indicate that temperature effects are present during the pulsation, while the EW varies by about 3%. The radius variation and acceleration curves have a small amplitude, indicating that the motion does not have any strong non-linear behaviour.