. Genetic, viral, and hormonal factors are involved in a pathogenetic mechanism that is manifest primarily as a disturbance in immunologic regulation. Recent studies on the sequential development of IgM and then IgC antibodies to DNA and RNA suggest that the thymus, spleen, and gonads exert important regulatory influences. We have found that sex hormones modulate the expression of autoimmunity in B/W mice, with androgens suppressing and estrogens accelerating disease. The hormones may act by restoring immunologic control.Animal models for human illness provide an unusual opportunity to study preclinical disease that is only rarely possible in human medicine. Such studies can lead to valuable insights into pathogenetic mechanisms underlying early events in disease and offer the hope of finding more specific and effective modes of prophylaxis or therapy.There are now several animal models for human lupus, including a new mouse strain called MRL, and a