Renal biopsy specimens of 15 patients with renal amyloidosis were studied by immunofluorescence microscopy. The amyloidosis was associated with chronic pulmonary disease in five, rheumatoid arthritis in one, chronic lymphocytic leukemia in one, and familial Mediterranean fever in five patients. In three patients no associated condition could be determined although the pattern of organ involvement resembled that of secondary amyloidosis. IgG and complement (C3) were demonstrated in the glomerular capillary walls and in the mesangium in all patients. The pattern of the deposits was neither granular nor linear. Ig and C3 appeared as large confluent masses or broad ribbon-like segments. In the six patients studied by electron microscopy the fibrillary formation of amyloid was seen in the mesangium and the glomerular capillary walls corresponding to the Ig deposits. No immunofluorescence or ultrastructural differences were observed among the patients with secondary, inherited and leukemia-associated amyloidosis included in this study.