Methods All patients and controls were Caucasian. Forty-eight pa-tients with IgA nephropathy and 19 patients with HSP were evaluated in Lexington, Kentucky. All patients with systemic disease such as systemic lupus erythematosus, vasculitis, chronic inflammatory disease of the liver, gastrointestinal tract, or skin were excluded. The diagnosis of IgA nephropathy was based on the demonstration by immunofluorescent microscopy of IgA as the predominant immunoglobulin in a mesangial distribution in the renal glomeruli. Some of these patients have been previously described [12]. Extensive pedigree data were available for all 48 IgA nephropathy patients. Eight of these patients were found to share common ancestors [13], but the closest relationship found for any individual was a great-greatgrandfather of one patient being the great-great-great grandfather of another. No patient with HSP is known to be related to another HSP or IgA nephropathy patient. The nineteen patients with HSP all had evidence of renal involvement as