hiPathDB provides two different types of integration. The pathway-level integration is a simple collection of individual pathways as described in the original database. We devised a gene-centric pathway model that could reflect different properties of four databases. The entity-level integration creates a super pathway that merged all pathways by unifying redundant components. Even though the detailed molecular information such as complex formation or modification can be lost in some cases, the merged superpathway provides a unified view of current knowledge on human pathways, which is critical to understand relationships among different pathways. Another strong merit of hiPathDB is the built-in pathway visualization module to support explorative study of complex networks in an interactive fashion. The force-directed layout algorithm is optimized for almost automatic visualization of pathways.