hybridcheck is a software package to visualize the recombination signal in large DNA sequence data set, and it can be used to analyse recombination, genetic introgression, hybridization and horizontal gene transfer. It can scan large (multiple kb) contigs and whole-genome sequences of three or more individuals. hybridcheck is written in the r software for OS X, Linux and Windows operating systems, and it has a simple graphical user interface. In addition, the r code can be readily incorporated in scripts and analysis pipelines. hybridcheck implements several ABBA-BABA tests and visualizes the effects of hybridization and the resulting mosaic-like genome structure in high-density graphics. The package also reports the following: (i) the breakpoint positions, (ii) the number of mutations in each introgressed block, (iii) the probability that the identified region is not caused by recombination and (iv) the estimated age of each recombination event. The divergence times between the donor and recombinant sequence are calculated using a JC, K80, F81, HKY or GTR correction, and the dating algorithm is exceedingly fast. By estimating the coalescence time of introgressed blocks, it is possible to distinguish between hybridization and incomplete lineage sorting. hybridcheck is libre software and it and its manual are free to download from .