PathWhiz is a web server designed for the creation of colourful, visually pleasing, and biologically accurate pathway diagrams that are machine-readable and interactive. As a web server, PathWhiz is accessible from almost any place and compatible with essentially any operating system. It also houses a public library of pathways and pathway components that can be viewed and expanded upon by its users. PathWhiz supports a high level of biological detail and complexity, using a specially designed drawing palette to render metabolites (including automated structure generation), protein_complexes (including quaternary structures, covalent modifications, and cofactors), nucleic acids, membranes, subcellular structures, cells, tissues, and organs. Both small molecule and protein_complex/gene pathways can be constructed quickly and intuitively by combining processes such as reactions, interactions, binding events, and transports. Pathway replication functionality allows existing pathways to be used as a basis for the creation of new pathways and for existing pathways to be automatically propagated across species. PathWhiz supports the generation of BioPAX, SBGN-ML, SBML, and PWML exchange formats, in addition to high resolution PNG, image map, and SVG images that can be explored using its interactive viewer. PathWhiz has been used to generate over 700 pathway diagrams for a number of popular databases including HMDB, DrugBank and SMPDB.