To study the population's composition of the bacterioplankton observed in the monimolimnion of the Lake Cadagno, we isolated the genes encoding the small subunit ribosomal RNA from a water sample taken at 17 meters depth, using PCR universal primers for the domain Bacteria. After cloning in a plasmid vector, 276 clones containing the 1.4 kb full-length insert were obtained, and further grouped by ARDRA (amplified rDNA restriction analysis) method. The phylogenetic position of 27 partial sequences derived from representative clones of ARDRA groups was established. These first results indicated that the bacterial community of the anoxic water layer of Lake Cadagno is composed at least by populations belonging to the Cytophaga/Flexibacter/Bacteroides group, the "Low G+C Gram-Positive Bacteria" group, the Spirochaetes group, and the Proteobacteria group. The majority of the partial sequences analyzed were affiliated to the alpha-4 subgroup of Proteobacteria.