Measurements have been carried out using the 50-MHz radar facility at Jicamarca/Peru applying the spaced receiver technique for investigating dynamical processes in the lower stratosphere. Using cross-spectrum analysis, an example of observations of significant velocity oscillations with a period of 4 minutes in the height range from 16 to 25 km is presented, which is interpreted as a propagating atmospheric gravity wave with an apparent horizontal phase speed of about 10 m s-1 and a vertical one of 200 m s-1. The observed period of about 4 minutes agrees quite well with the V¿is¿l¿-Brunt period for that height range.