Experiments are carried out to investigate the structure of a double diffusive interface separating two layers in a laterally heated enclosure. Due to the differential heating of the enclosure sidewalls, a circulating flow is induced in each layer such that the interface is simultaneously exposed to a velocity shear and double diffusive convection. The main goal of this work is to study the structure of the interface and some of its instability characteristics. The experiments are carried out in a box with inner length, width and height dimensions of 100 x 100 x 92 mm. The velocity field at the vicinity of the interface is measured by a PIV system. Vertical concentration and temperature profiles are measured using a micro-scale conductivity/temperature instrument and the flow is visualized using the schlieren technique. Analysis of mean horizontal velocity profiles, obtained at different times during the experiment, illustrates the increasing tilt of the interface with time. Spectral analyses of velocity perturbations under unstable and stable conditions confirm the existence of the coherent vortices observed by the schlieren technique. The vortices above and below the interface are associated with different dominant frequencies due to the asymmetric character of the flow. Measurements show that the vortices are generated outside the region of the stabilizing concentration profile by a mechanism, which is essentially thermal and similar to Rayleigh-Benard instability with weak shear. (c) 2005 Elsevier Ltd. All rights reserved.