We experimentally tested the hypothesis that simulated rainfall would trigger higher levels of activity in soil biota under large surface accumulation of litter in a Chihuahuan desert soil. Bacterial biomass was highest on days 6 and 12 in plots receiving simulated rain and increased with increasing litter. The turnover of themicrobial biomass was estimated as 6.97 days and was independent of either water or litter quantity. Soil respiration was higher in the wet treatments on days 0 and 6. When treatments were averaged across time, the highest soil respiration was in the 150 g m-2 litter, watered plots. The same pattern was observed in the dry treatments after natural rain events. On day 6, protozoa were higher in the wet plots; protozoa in the dry plots were 100% cystic while those in the wet plots were 100% trophic. Protozoan numbers were independent of litter quantity and reached the maximum on day 18. Amoebae were the dominant protozoa with an average population size of 25,000 g-1. Flagellates were intermediate in numbers (4,900 g-1) while ciliates were the least abundant (700 g-1).