A comparative study is presented of the microflora of sediments in three caves with different trophic characteristics. Quantitative and qualitative variations of microflora were investigated for one year by studying the total microflora and the activity of the nitrogen cycle functional groups. Data were compared with those of other works of previous authors. Results show that the quantity and kind of organic matter of sediment are most important factors regulating the abundance and activity of cavernicolous microflora. The experimental part of this paper is prefaced by a digest of investigations previously carried out on cavernicolous microflora and by a report of topographic, geomorphologic, hydrologic and trophic characteristics of the caves examined.