Studies of biological systems are often facilitated by diagram models that summarize the current understanding of underlying mechanisms. The increasing complexity of our understanding of biology necessitates computational models that can extend these representations to include their dynamic behavior. We present here a new tool we call Synthesizing Biological Theories which enables biologists and modelers to construct high-level theories and models of biological systems, capturing biological hypotheses, inferred mechanisms, and experimental results within the same framework. Among the key features of the tool are convenient ways to represent several competing theories and the interactive nature of building and running the models using an intuitive, rigorous scenario-based visual language. The defnition of the modeling language is geared towards enabling formal verifcation and analysis.