It is widely accepted that developing T cells can undergo clonal deletion in the thymus in response to a high affinity self-Ag. This is largely based on studies of TCR transgenics. However, encounter with high affinity self-Ag can also result in receptor editing in TCR transgenic models. Because all TCR transgenics display ectopic receptor expression, the tolerance mechanism that predominates in normal mice remains an open question. When self-Ag drives receptor editing during T cell development, one expects to find in-frame, self-reactive TCRα joins on TCR excision circles (TRECs), which are the products of secondary V/J recombination in the TCRα locus. Such joins are not expected if clonal deletion occurs, because the progenitor cell would be eliminated by apoptosis. To test the relative utilization of receptor editing vs clonal deletion, we determined the frequency of in-frame, male-specific joins on TRECs in male and female HYβ transgenic mice. In comparison with female HYβ transgenic mice, our analysis showed a lower frequency of TRECs with male-reactive V17J57 joins in male mice. Thus, it would appear that receptor editing is not a predominant tolerance mechanism for this self-Ag.