MOTIVATION: Riboswitches are short sequences of messenger RNA that can change their structural conformation to regulate the expression of adjacent genes. Computational prediction of putative riboswitches can provide direction to molecular biologists studying riboswitch-mediated gene expression. RESULTS: The Denison Riboswitch Detector (DRD) is a new computational tool with a Web interface that can quickly identify putative riboswitches in DNA sequences on the scale of bacterial genomes. Riboswitch descriptions are easily modifiable and new ones are easily created. The underlying algorithm converts the problem to a 'heaviest path' problem on a multipartite graph, which is then solved using efficient dynamic programming. We show that DRD can achieve ∼ 88-99% sensitivity and >99.99% specificity on 13 riboswitch families. AVAILABILITY AND IMPLEMENTATION: DRD is available at http://drd.denison.edu.