Abstract Summary: Knowledge of pathogen–host protein interactions is required to better understand infection mechanisms. The pathogen–host interaction search tool (PHISTO) is a web-accessible platform that provides relevant information about pathogen–host interactions (PHIs). It enables access to the most up-to-date PHI data for all pathogen types for which experimentally verified protein interactions with human are available. The platform also offers integrated tools for visualization of PHI networks, graph–theoretical analysis of targeted human proteins, BLAST search and text mining for detecting missing experimental methods. PHISTO will facilitate PHI studies that provide potential therapeutic targets for infectious diseases. Availability: http://www.phisto.org. Contact: saliha.durmus@boun.edu.tr Supplementary information: Supplementary data are available at Bioinformatics online.