Abstract: The present invention relates to a method for measuring de novo T-cell production in humans, and more particularly to the assessement recent thymic emigrant (RTE) diversity in a T-cell sub-population of a patient by the detection of T-cell receptor &bgr; chain DNA deletion circles (TCR&bgr;DC) generated during TCR gene rearrangement of thymocytes in the thymus. The method comprises isolating a T-cell sub-population from a patient, extracting genomic DNA from the T-cell sub-population, amplifying the genomic DNA with a primer specific for a T-cell receptor &bgr; chain DNA rearrangement deletion circle (TCR&bgr;DC) family and detecting the TCR&bgr;DC, the TRC&bgr;DC being indicative of the presence of a RTE. The method assesses the quantitative and qualitative (diversity) intrathymic T-cell production by quantitating the relative frequency and diversity of RTEs within various sub-populations of circulating human T-cells.