The etiopathogenesis of systemic lupus erythematosus remains an enigma that will probably not be solved until the genetic basis for susceptibility is defined. Through genomewide searches, we have provided a foundation for this by identifying and characterizing loci predisposing to specific disease traits in four major lupus-susceptible mouse strains. Further ongoing work that includes the study of interval-specific congenic lines and precise mapping of loci should lead to identification of the corresponding genes and elucidation of processes critical for disease pathogenesis. Another important area of investigation is the study of cell-cycle and apoptosis genes in systemic autoimmunity and aging. Based on earlier work, we proposed that the characteristic overexpansion of memory phenotype cells in these conditions may be owing to replicative senescence. Understanding the molecular mechanisms that regulate the generation of these cells may permit selective manipulations to control this process. Other areas of investigation that we are actively engaged in are the role of T cell receptor repertoire in disease and the definition of cellular genes affected by infection with human immunodeficiency virus.