Carbon dioxide exchange rates (CERs) of all leaves along the stem of northern red oak (Quercus rubra L.) seedlings (a leaf insertion gradient or profile) were determined at several stages of ontogeny. Seedlings were grown and measured under growth chamber conditions favorable for the production of multiple flushes of shoot growth. The CERs were measured with a portable closed-circuit CO2 analyzer at ambient photosynthetic photon flux densities and were determined for every leaf of each seedling. Carbon dioxide exchange rates per unit projected area of individual leaves (CERA) increased along leaf-maturation gradients in expanding flushes. After flush growth was completed, all leaves of a flush has similar CERA. However, because median flush leaves were the largest, they accounted for the greatest proportion of an expanded-flush's CER. First-flush leaves were the major contributors to total seedling CER through the second flush of growth--encompassing half of the period required to produce a three-flush oak seedling. This study's data, based on short-term CER measurements, showed ontogenetic patterns of CO2 exchange similar to those reported for northern red oak under "steady state" laboratory conditions. For. Sci. 34(1):69-76.