While studying the microbial flora of Lake Cadagno, a meromictic alpine lake, a peculiar morphological group of bacteria, named "morphotype R ", was observed. This group of bacteria was present only in the anoxic monimolimnion. Its distribution in the water column could be correlated with the hydrogen sulfide content and the redox potential. Attempts made to culture cells of the morphotype R failed, but it has been characterized by optic, fluorescence, and transmission electron microscopy. As far as the size, the shape, and the habitat were concerned, morphotype R cells appeared similar to disparate non-culturable bacteria of anoxic waters (morphotypes T5, R1, and R2) described by other authors. Since the morphotype R represented on average up to 30% of the total microbial flora in the monimolimnion of Lake Cadagno, further ongoing studies aim at assessing the taxonomy as well as the ecological significance of this microbial population.