Eight perennial C-4 grasses from the Jornada del Muerto Basin show 5-fold differences in relative growth rates under well-watered conditions (RGR_max). In a controled environment, the hypothesis was tested that there is an inverse relationship (trade-off) between RgR_max and the capacity of these species to tolerate drought. Based on these controlled-environment results, it is hypothesized that the commonly reported correlation between plant growth potential and drought tolerance in the field may in some cases be explained by differential effects of plants on soil-water content rather than by differences in species responses to drought.