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The faunal composition and changes in the vertical distribution patterns of soil mites and other microarthropods were described and monitored over an 18-h period at a site in the Negev desert of southern Israel. There was an overwhelming predominance of prostigmatid mites (55%) compared with Cryptostigmata (33%) in the collections. Specific determinations on the Cryptostigmata indicated that taxa, which could be identified as Mediterranean, made a sizeable contribution to this fauna. Microarthropod densities in general, and those of Prostigmata, Cryptostigmata and Mesostigmata in particular, compared favourably with those recorded from other arid desert sites in N. America and Australia. Prior to the sampling period which commenced at 6 p.m., the site was exposed to the drying effects of the Khamsin wind. Microarthropod populations were mainly located at depths below 6 cm during the following 18-h period, and this may be interpreted as an avoidance of the arid conditions obtaining at the surface, particularly during the hours from 6 p.m. to midnight. Soil temperatures remained low after midnight, but the relative humidity above the soil increased to 90% and there may have been some internal dew formation in the soil surface horizon at this time. There is some evidence of an upward movement of prostigmatid and cryptostigmatid mites as a response to increasing levels of humidity in the surface horizon during this period. We suggest that this study confirms the findings of Whitford et al. (1981) that soil microarthropods are sensitive to changes in soil moisture characteristics which operate on a diurnal scale.