The complexities of biological simulation present difficulties with modeling and experimenting. Simulators process models represented as code, whereas biologists think about abstract models. Our ModelBrowser addresses this difficulty through interactive visualization. Variables and equations appear as a directed graph of nodes and edges, and the user can search and browse this graph by performing queries on metadata associated with the variables and the connectivity of the edges. The browser also supports a hierarchical categorization of the variables, such as by an ontology. We believe that the ModelBrowser will help biologists reason about code in the context of the abstract model, so that they can understand and modify others' code and debug their own.