A wind tunnel experiment was conducted to investigate the effects of three high-rise building configurations on the diffusion of emissions released near the downstream base of the buildings. The building configurations included an isolated high-rise building, two high-rise buildings separated in the streamwise direction, and two high-rise buildings separated in the streamwise direction, but situated atop a terrace-shaped lower level. For each configuration, the emission source location, building height and/or building separation was systematically varied while tracer concentration measurements were obtained both downstream and on the surface of the buildings. When the source was within the downwind wake of the twin building models, the source elevation did not strongly influence the building surface distributions although the maximum concentrations appeared at different elevations. Compared to the effect of an isolated building, the twin buildings resulted in higher concentrations in the near-wake of the downwind building.