Adrenomedullin, a recently discovered peptide with hypotensive effects, has been shown to be elevated in glomerular diseases. In this study, we investigated the relationship between the plasma adrenomedullin and renal tubulointerstitial lesion in patients with mesangial proliferative glomerulonephritis. Twenty-six patients with a normal renal function, diagnosed histologically with mesangial proliferative glomerulonephritis with (n = 1) or without immunoglobulin A composure (n = 25), were enrolled in this study. Eighteen healthy volunteers were enrolled as controls. Patients were divided into two groups according to the degree of tubulointerstitial lesion. Plasma adrenomedullin level was measured by an adrenomedullin-specific radioimmunoassay. Plasma adrenomedullin concentrations were higher in patients with mesangial proliferative glomerulonephritis than in healthy volunteers (5.71 × 10 −12 ± 0.37 × 10 −12 vs 2.12 × 10 −12 ± 0.15 ×10 −12 mol/L; p<0.01). Plasma adrenomedullin was also higher in patients with severe tubulointerstitial lesion than those with mild lesions (6.69 × 10 −12 ± 0.25 × 10 −12 vs 4.58 × 10 −12 ± 0.13× 10 −12 mol/L; p<0.01). Plasma adrenomedullin concentrations increase in patients with mesangial proliferative glomerulonephritis, and the degree of elevation correlates with tubulointerstitial lesion.