The HH 80-81 complex is the largest and most powerful stellar jet system of high collimation known. We have obtained second-epoch (1994.3) VLA observations of the HH 80-81 thermal radio jet and compared them with previous observations made 4.1 yr before (1990.2). Both sets of observations were made at 3.5 and 6 cm with an angular resolution of ∼0"3. Large proper motions have been detected in the condensations along the jet. These proper motions are in the range of 70-160 mas yr-1, equivalent to 600-1400 km s-1 at the distance of 1.7 kpc of the source. Such large velocities have not been previously measured in the context of jets from young stellar objects, and they give support to the identification of the powering source of this Herbig-Haro complex as a very massive star. Between the two epochs of observation, an ejection event created two new knots in the jet flow that in 1994.3 appear symmetrically projected at only 500 AU from the central source. The existence of significant clumpiness and symmetry in the jet so close to the star gives support to the notion that disturbances in stellar jets are produced by the driving source, and not as a result of instabilities produced later in the flow.