Abstract. Many de novo assembly tools have been created these last few years to assemble short reads generated by high throughput sequencing platforms. The core of almost all these assemblers is a string graph data structure that links reads together. This motivates our work: BlastGraph, a new algorithm performing intensive approximate string matching between a set of query sequences and a string graph. Our approach is similar to blast-like algorithms and additionally presents specificity due to the matching on the graph data structure. Our results show that BlastGraph performances permit its usage on large graphs in reasonable time. We propose a Cytoscape plug-in for visualizing results as well as a command line program. These programs are available at http://alcovna.genouest.org/blastree/.