We present the results of 3.5-cm delay-Doppler and Doppler-only (continuous wave or CW) radar experiments to assess three potential Mars Pathfinder landing sites: Ares Vallis, Tritonis Lacus, and northwest (NW) Isidis. The regional relief at all of the landing sites is appropriate for a Pathfinder landing sequence: east-west slopes do not exceed 3¿ at any of the sites. We find that Ares Vallis has a Hagfors rms slope of &thgr;rms=4.8¿¿1.1¿ as measured by delay-Doppler radar, and &thgr;rms=6.4¿¿0.6¿ measured by CW radar. These values are similar to, or less than the previous measurements of the Viking Lander 1 region. The Tritonis Lacus landing site is rougher with delay-Doppler, &thgr;rms=5.6¿¿0.6¿, while the NW Isidis landing site is very smooth, both in a regional sense (slopes <0.7¿) and in a Hagfors rms slope sense: &thgr;rms=1.8¿¿0.2¿. Reflectivities at all of the sites should be sufficient to allow the radar altimeter on Pathfinder to function properly.¿ 1997 American Geophysical Union