A wind-tunnel study has been conducted to examine the effects of several parameters on the downwash of effluents released from stacks in the vicinity of rectangular-shaped buildings. The situations modeled included idealized or generic steam-boiler and combustion-turbine electric-generating plants. Systematically varied were parameters such as the stack height, location of stack, wind direction, effluent-speed to wind-speed ratio, and effluent buoyancy. Measurements included over 300 concentration profiles. Vertical profiles were measured at a fixed distance downwind, both in the presence and in the absence of the buildings, to ascertain the building effects. In several of the more interesting cases, more extensive measurements were made to more fully describe the entire concentration field.