I describe the vertical distribution of root biomass and root productivity in a xeric shrubland of central Mexico. The effect of the soil nitrogen on root production was evaluated with a fertilization experiment. The highest percentage of roots was found at a depth of 40 to 60 cm. Monthly variation in root biomass for diameter class was significant. Fine and very fine roots were the most important fraction in terms of biomass and production. The highest production of fine root occurred in native soil versus the other treatments.