Samples collected in Mammoth Cave, Kentucky, revealed the presence of a diversified but not too abundant diatom community in the cave. As the material was not subjected to culturing experiments but was investigated immediately after arrival, both in native and permanent preparations, it was possible to: 1. ascertain that the majority of the diatoms contained well developed, apparently healthy and functioning chloroplasts and 2. to get a rough estimate of the actual number of specimens present in a microhabitat. The identifications resulted in the recognition of 16 diatom taxa of which possibly 4 are new to science. Further studies are, however, required to ascertain this point.