We investigated CD56+ cells (natural killer cells), CD14+ cells (macrophage) and CD3+ cells (pan T cells) in urine using flow cytometry in various renal diseases including idiopathic crescentic glomerulonephritis, IgA nephropathy, membranoproliferative glomerulonephritis membranous nephropathy, pyelonephritis and idiopathic renal hematuria. A remarkable increase of CD56 cells in urine was observed in glomerulonephritis with marked necrotizing/and or crescentic (NC) lesions. The ratio of CD56+ cells/CD3+ cells was correlated with the severity of NC lesions. The ratio of CD14+ cells/CD3+ cells was increased in glomerulonephritis with endocapillary proliferation. Using immunohistochemical methods, CD56+ cells were also observed to be present in cellular crescents in biopsy specimens. These observations suggest that an analysis of these cells in urine using flow cytometry may be a useful tool for monitoring disease activity in proliferative glomerulonephritis.