Edena (Exact DE Novo Assembler) is an assembler dedicated to process the millions of very short reads produced by the Illumina Genome Analyzer. Edena is based on the traditional overlap layout paradigm. All exact overlaps between any pair of reads are computed and structured in a graph (overlap step). Basically, the reads are indexed in a prefix array and overlaps are revealed by dichotomic search in the arrays. The graph is then analyzed to remove transitive and spurious edges (layout step). Finally, contigs that can be assembled following unambiguous path in the graph are given as output. Edena allows to produce contigs of several kbp with a near full coverage of the bacterial genome being sequenced. Registration not required.