BIOMOD is a user-oriented, interactive computer graphics system using a terminal composed of a RAND Tablet, CRT, and keyboard. The background computer is currently an IBM 360/65; the system uses a 228K partition of high-speed core with overlay from disk. The system was designed so that a user untrained in computer programming could have direct access to the computer to design a model of a biochemical or physiological system and subsequently simulate his problem. He constructs his model using semiformal simulation languages, insofar as possible from his own discipline. After construction, the model is automatically compiled for simulation. Programs in the computer translate each detail of the model into Continuous Systems Modeling Program (CSMP) language, an IBM program that in turn compiles it into FORTRAN and finally machine language. CSMP also organizes the problem for solution.