Abstract: A method for diagnosing autoimmune disease in mammals, including humans, is described. A blood sample is collected from a subject, and mononuclear white blood cells separated therefrom. The mononuclear cells then are cultured in vitro. Patients with autoimmune disease develop characteristic white cell aggregates with autophagocytosis in the culture. Mononuclear cells from normal patients do not exhibit this cell aggregation with autophagocytosis.