The effects of supplemental water supplied as large events, 25 mm per month, or as frequent small events, 6 mm per week, and available nitrogen on density, aboveground biomass and species composition of an annual plant community were studied in the northern Chihuahuan Desert. The amendments of water an N had no effect on total annual plant density. However, supplemental water resulted in increased density of eight species and nitrogen fertilization produced increased densities in nine species. Total aboveground biomass was higher in the nitrogen fertilized plots; water amendments had no effect on dry matter production and there were no significant water-nitrogen interactions. Cluster analysis showed that species composition was similar on the fertilized plots and that the plots receiving 25 mm month-1 additional water in a single event differed most from the others. Species richness was highest in the 6 mm week-2 , unfertilized plots, and lowest in the unwatered-unfertilized plots. Biomass production of six of the 23 species recorded was significantly increased by nitrogen fertilization and biomass of two species was significantly reduced.