We have analyzed different parameters of the interleukin 2 receptor (IL2R) traffic in a murine IL2-dependent T cell line, B6.1. These cells express about 10(5) IL2R, of which approximately 10% are of high affinity (HAR). About 90% of all mature immunoprecipitable receptor molecules in the cell are on the cell surface. Measurements of the half life and of the rate of receptor synthesis indicate that these cells produce approximately 500 receptor molecules per cell and min. IL2 deprival for less than 6 h does not affect this rate. B6.1 cells internalize IL2 via their HAR only, with a maximal rate of about 500 molecules per cell and min. Among the receptors present at a given time on the cell surface, about 15% are internalized within 30 min. Receptor internalization is independent of IL2. The data obtained argue against rapid recycling of the HAR. The rate of receptor synthesis can be reconciled with the rate of IL2 internalization and the observation that internalization occurs only via HAR by assuming that cell surface low-affinity receptors can be transformed into HAR by associating with other molecules.