Winds in the Martian atmosphere at altitudes from 1.5 to 3.5 km have been determined from parachute descent trajectories of the two Viking landers. Viking 2 reached equilibrium with nearly steady winds of ~8 m/s to the southeast below 3.3 km at 1000 LT. Viking 1 winds at 1615 LT were generally to the northwest at ~20 m/s, but the wind vector rotated clockwise with decreasing altitude. At 1.5 km, the Viking 1 wind direction was close to that measured by the landed anemometer at the same local time, while at the Viking 2 site, wind direction at 1.5 km was nearly opposite that near the surface. This is consistent with the fact that Viking 1 descended within a vigorously convective boundary layer, while Viking 2 at 1.5 km was above the boundary layer. Turbulent velocities in the Viking 1 boundary layer were ~3 m/s. Mean upflow velocity was ~1 m/s. The Viking 2 atmosphere was relatively quiescent, with orderly wind directional variation possibly suggesting the presence of waves. Comparison of the measured winds with a recent global circulation model showed little or no correspondence, probably an indication that the winds were locally controlled. The boundary layer, slope-wind model of Haberle et al. (1993), with ground slope adjusted to give best fit to these and landed meteorology data, gave roughly the wind direction and the observed magnitude within a factor of ~2, but with opposite rotation of the wind vector with altitude. The ground slopes deduced are consistent with terrain observed in approach to the Viking 1 landing, and do not conflict with the less definitive terrain data at the Viking 2 site. The high sensitivity of winds at altitudes up to several kilometers to terrain slopes as small as a few meters per kilometer would suggest that slope winds may be widely found in the lowest few kilometers of Mars atmosphere. ¿ American Geophysical Union 1993