Mites were more abundant than Collembola in all sites except in Prosopis litter from the edge of a playa. At this site, collembolan density was estimated to be 24 460/m2. Four orders of mites occurred in the sites surveyed: Prostigmata, Cryptostigmata, Mesostigmata and (infrequently) Astigmata. Mesostigmata were numerous only in Atriplex litter. Prostigmata and Cryptostigmata were equally abundant only in the litter under Prosopis and on the bajada site and mineral soil under Fallugia. Elsewhere, Cryptostigmata tended to be more numerous than Prostigmata where the organic content of the substratum was high (>30%) and vice versa. The highest total mite density occurred in the Juniperus litter (29 486/m2), the lowest in Larrea litter (8274/m2). An Index of Diversity, calculated for the various groups of microarthropods at the 12 sites, was very variable. The equitability component of this species diversity provided a good indicator of the relative stability of the sites studied.