The development of double-negative (CD4-, CD8-) T cells and other T cells subsets in lymphoproliferation (lpr) mice continues to be poorly defined. Recent studies indicate that lpr is a mutation of a receptor mediating apoptosis. It has thus been hypothesized that T cell development in the thymus should be abnormally affected. In this study, we analyzed the TCR V beta repertoire of double-negative T cells as well as CD4+ and CD8+ single-positive subsets in various lpr and matched non-lpr strains. Particular comparisons were made to determine the influence of different class I and class II molecules on repertoire formation. The data demonstrate that positive and negative selection of the CD4+ and CD8+ subsets are normal in lpr mice when compared with non-lpr congenic mice. Surprisingly, the result also suggest that double-negative T cells are mostly selected on class I MHC molecules in a pattern similar to the CD8+ population, and that T cells positively selected on class II MHC antigens may be absent from the double-negative population. In all lpr strains, we also found an increased percentage of double-negative V beta 8.3+ cells out of proportion to levels in the CD4+ or CD8+ subsets. Longitudinal studies and studies in thymectomized animals showed that this increase reflects a peripheral process selectively affecting V beta 8.3+ double-negative T cells. Together, these repertoire data provide new insight into the effect of the lpr genetic defect on T cell development and the derivation of double-negative T cells. Despite the role of Fas in apoptosis and the abnormal expression of this gene in lpr mice, the present results support the hypothesis that thymic events are relatively normal in lpr mice, and that the double-negative T cells are mostly class I MHC selected and expanded by abnormal peripheral processes.