SOYCHMBR. I, a model designed to study plant growth in a closed chamber, has been developed based on the work of Meyer et al. and their model SOYMOD/OARDC. In the development of SOYCHMBR. I, SOYMOD/OARDC has been modified to allow for incorporation of plant-chamber interactions that are important in the closed environment and to update the model so that it adequately represents the current understanding of plant processes. The photosynthetic routine has been replaced by Tenhunen's. The present version of SOYCHMBR. I is described, and the CO2 dynamics in three test runs are discussed.