PSAR-Align: improving multiple sequence alignment using probabilistic sampling. We developed PSAR-Align, a multiple sequence realignment tool that can refine a given multiple sequence alignment based on suboptimal alignments generated by probabilistic sampling. Our evaluation demonstrated that PSAR-Align is able to improve the results from various multiple sequence alignment tools. Availability and implementation: The PSAR-Align source code (implemented mainly in C++) is freely available for download at