The theoretical behaviour of the near-surface wind-driven currents is strongly dependent upon the models used to describe the mixed surface layer (especially the kinematic viscosity profile). This paper investigates measurements of ocean currents by HF Doppler radars in order to shed some light on this problem. It is found that the relative directions of the wind and current velocities and the variation of the current speed with respect to radar frequency (i.e. with respect to depth) are the most sensitive parameters to analyse for discriminating among the various models. The results of a preliminary experiment which was conducted in the western Mediterranean during the autumn of 1981 are presented. In this experiment the current was measured on 8 consecutive days at two radar frequencies corresponding to integration depths of 1 and 2 m, respectively. A special study shows that the near-surface current is only weakly influenced by the proximity of the coast (the measurements were obtained between 10 and 34km offshore). Because of the shortness of the experiment analysis of the wind-current relation does not provide the required accuracy whereas analysis of the current shear, which can process simultaneously the data obtained in nine different sea cells, gives a significant result supporting models with small shears (like Ekman's model with a constant kinematic viscosity profile). Some future improvements are briefly discussed.