PLANT productivity in deserts can be nitrogen-limited. Nitrogen inputs are often low, soil nitrogen pools small, and losses from runoff, erosion, volatilization and denitrification, can be high1-6. We have now found an unusual, important source of soil nitrogen in the Central Negev Highlands of Israel, a limestone rock desert with patches of soil (Fig. 1). Snails feed on endolithic lichens that grow within the rock, ingesting both rock and lichens7,8, and depositing their faeces on the soil under the rocks. Snails transfer between 22-27 mg nitrogen per m2 per year to soil, which constitutes about 11% of total soil nitrogen inputs, at least 18% of net soil inputs, and a minimum of 27% of the nitrogen annually accumulated by endolithic lichens from dust. The substantial contribution of snails to the nitrogen cycle is probably important for higher plant production.