Evidence is presented for the existence of a wave number 3, westward traveling 2-day oscillation in the temperature measurements made by the Nimbus 5 SCR and Nimbus 6 PMR instruments. The wave has largest amplitude in the mesosphere at low latitudes of the summer hemisphere and has a markedly asymmetrical meridional structure. It is suggested that the wave may be a free wave similar to the 5-day wave identified in Nimbus 5 SCR data by Rodgers (1976). The veritcal structure shows little phase tilt and a slight indication of an increase in amplitude with height.