In 1997, the classical argentine geodetic system Campo Inchauspe 69 was replaced by POSGAR 94 (POSiciones Geodesicas ARgentinas), a realization of WGS84 through GPS observations. After the SIRGAS reference frame was available, POSGAR was recomputed following the guidelines given by the SIRGAS working group II. The resulting new frame, termed POSGAR 98, realizes the International Terrestrial Reference System (ITRS). The main scope of this paper is to assess the precision and accuracy of the vertical component for both the 94 and 98 frames. The investigation was carried out using several independent GPS data sets. The results show almost randomly distributed errors of up to 1 m for POSGAR 94. The improvement in the heights is more than ten times when POSGAR 98 coordinates are considered.