An improved digital computer model of the neonatal respiratory system was developed. Using previous models as a basis, important improvements were made in order to accurately simulate infant blood gas chemistry and its effect on respiratory and circulatory control. The model is divided into five physiologic compartments: heart, brain, lungs, tissues, and cerebrospinal fluid compartment. Respiration is a function hydrogen ion concentration in the medulla and oxygen tension and hydrogen ion concentration in the aorta. Cardiac output is a function of oxygen and carbon dioxide tension in the brain and oxygen tension at the tissues. Major improvements in this model include an advanced carbon dioxide dissociation relationship and a complex blood buffer system. It also is able to simulate treatment of respiratory distressed infants with bicarbonate infusion and respirator therapy. In addition, it has a simplified variable time delay. In order to evaluate the model, an attempt was made to simulate an actual infant. Results indicate that while the model is an improvement over previous attempts, it is still deficient in some areas in its ability to simulate actual infants. More comparisons with actual data must be made to accurately evaluate the model. / Master of Science