Laboratory experiments were conducted in straw fuel beds in order to characterize the effect of a widely used long-term retardant on fire behavior under different conditions: no slope–no wind, upslope–no wind, and no slope–upwind. The results are reported in terms of reduction factors for a set of variables characterizing fire behavior. In the experimental conditions the values of upslope–no-wind and no-slope–upwind fires showed no statistically significant differences from those of no-slope–no-wind fires. For all types of fire, values obtained for the reduction factors on rate of spread, fuel consumption ratio, fire intensity, and flame length were 63%, 36%, 77%, and 54%, respectively.