Current knowledge on the consequences of wildfire for faunistic biodiversity is fragmentary, particularly as regards deciduous forests south of the Alps, which is the region of Switzerland most affected by this phenomenon. After the first year of a three year doctoral thesis about "the effects of wildfire on invertebrate biodiversity", we present the project and some preliminary results about spiders. The investigation is being conducted in a hilly region in the "chestnut belt" (Castanea saliva forest). The study area is on a south-facing slope. So far we sampled several invertebrate groups in 23 test areas: 7 areas affected by a single fire, 10 areas with repeated fires, and 6 control areas of intact forest. The soil fauna were assessed using several standardised sampling methods: pitfall traps for epigeic arthropods, litter-soil samples and soil eclectors for soil dwelling groups, and yellow window traps for flying insects. The fauna was sampled between January and October 1997. The data in the sample and the control areas, as well as in the burned surfaces of different age and those burned several times have been compared statistically. Only individuals identified down to the species level have been included in the analysis. The first results show that fire regime has a significant effect on spider populations and spider composition. Some species are already present a few days after the fire. However, other species seem to avoid burned areas. Surfaces which have been burned several times show the highest species diversity after 2 years' regeneration. Later (six years after the last fire), the diversity of spiders declines and reaches the values found in the control area (not burned for more than 30 years). Some first hypotheses about these preliminary results are presented.