Using immunofluorescence, we studied 19 patients with IgA nephropathy to determine whether the expression of intercellular adhesion molecule (ICAM)-l in glomeruli might reflect the disease activity. The relationship between the expression of ICAM-1 and the infiltration of lymphocytes, monocytes and polymorphonuclear leukocytes (PMN) in glomeruli of IgA nephropathy cases was examined. The expression of IC AM-1 in patients in the advanced stage was significantly higher than that in patients in the mild stage. In double immunofluorescence, the distribution of ICAM-1 expression in glomeruli was different from that of IgA deposition in patients in both stages. Glomeruli which showed increases of ICAM-1 expression had marked infiltration of lymphocytes (OKT4+, OKT8+ T cells), and monocytes (OKM1+ cells). Increase of urinary protein and decreases in renal function were observed in patients in the advanced stage. It appears that the expression of ICAM-1 is closely linked to glomerular cell proliferation, and infiltration of lymphocytes and monocytes in patients with IgA nephropathy. However, the expression of ICAM-1 in glomeruli might not be correlated with IgA-dominant immune complexes in this disease.