HoPaCI-DB (Host-Pathogen Interaction database) is a manually curated database of interactions between host-pathogen-related elements such as biomolecules (proteins, metabolites etc.) and other factors (biological processes, cellular components etc.). HoPaCI-DB is an analysis resource for the study of the pathogens Pseudomonas aeruginosa and Coxiella species. The majority of host species refers to mammalia, but also results from experiments with C. elegans, Drosophila melanogaster or Danio rerio are included. The aim of HoPaCI-DB is to serve as knowledge base for experimentally- oriented scientists and as resource for bioinformatics applications.