  Motivated by the observation of a giant Nernst effect in URu_2Si_2, the
thermoelectric response of the related system UPt_2Si_2 was investigated using
thermal and electric transport properties such as the Nernst and Seebeck
effects, thermal conductivity, Hall effect and electrical resitivity. Unlike
URu_2Si_2, UPt_2Si_2 is neither superconducting nor exhibits a ``hidden-order''
state. Nevertheless a pronounced Nernst effect anomaly is found to coincide
with the onset of the antiferromagnetic order in UPt_2Si_2. Although the
absolute values are substantially lower, its appearance and characteristics can
favorably be compared to the giant Nernst effect in URu_2Si_2 indicating the
common feature of a partial Fermi surface gap.
