In order to gain a better understanding of the mixing process, simultaneous measurements of velocities and concentrations would be helpful. Therefore experiments were carried out by means of simultaneous PIV and LIF measurements on the mixing of a point source placed at the centreline of a turbulent pipe flow. The PIV and LIF measurements do not influence each other. The results are used to determine the concentration velocity correlation term present in the time averaged Reynolds equation of the concentration field. In addition we study the effect of coherent structures on the mixing process. This can be done by doing conditional averaging of the time series.