We describe a dedicated RNA motif search program and web server to identify RNA riboswitches. The Riboswitch finder analyses a given sequence using the web interface, checks specific sequence elements and secondary structure, calculates and displays the energy folding of the RNA structure and runs a number of tests including this information to determine whether high-sensitivity riboswitch motifs (or variants) according to the Bacillus subtilis type are present in the given RNA sequence. Batch-mode determination (all sequences input at once and separated by FASTA format) is also possible. The program has been implemented and is available both as local software for in-house installation and as a web server at http://www.biozentrum.uni-wuerzburg.de/bioinformatik/Riboswitch/.