We have developed a computer software package for Macintosh to simulate the metabolism and hemoglobin binding affinity of human red blood cell. The model is capable of simulating hemoglobin binding of ligands, metabolite concentrations, and metabolic fluxes at physiological steady state and in response to extracellular parameter variations, such as pH, osmolarity, glucose, and adenine concentrations. The kinetic parameters of enzymes, extracellular conditions, and initial intracellular metabolite concentrations can be specified by the user in order to model a particular situation. The software is use friendly, utilizing menu, window, and mouse to interact with the user. It also provides a pathway map of the red cell, which allows a direct access to enzyme kinetics by clicking the enzymes in the map.