Fifteen men (average age 54.6 +/- 14.6 years) with IgA-associated glomerulonephritis underwent concomitant skin and renal biopsies to clarify any potential diagnostic relationships. Both types of tissues were studied by standard light, immunofluorescent, and electron microscopic techniques. The glomeruli of all the patients studied showed renal mesangial IgA deposits. All corresponding skin biopsy specimens showed no IgA deposition in the cutaneous blood vessels. The negative association suggests that examination of the skin biopsy specimen alone is not reliable in establishing the diagnosis of primary IgA nephritis. In view of the known skin involvement in Henoch-Schönlein nephropathy, we propose that skin biopsy specimens be examined routinely when renal biopsy specimens demonstrate IgA deposits, to differentiate primary IgA nephropathy from a forme fruste of Henoch-Schönlein purpura.