A collection of computationally predicted R-loop forming sequences (RLFSs). R-loopDB is a comprehensive database of RLFSs in eight organisms, i.e. human, chimp, mouse, rat, chicken, frog, fruit fly and yeast, that offers benefits for the researchers who study R-loop related human diseases using these species. The combination of several other data resources, such as RLFS strand, GC skew value and experimental R-loop detection data, could provide more information for advanced analyses and predictions. R-loopDB allows searching of RLFSs in the genes and in the 2 kb upstream and downstream flanking sequences of any gene. R-loopDB exploits the Ensembl gene annotation system, providing users with chromosome coordinates, sequences, gene and genomic data of the 1,565,795 RLFSs distributed in 121,056 genic or proximal gene regions of the covered organisms.