['To assess the influence of incipient diabetic nephropathy on the levels of total renin in serum.', 'Fifty-five adult patients with insulin-dependent diabetes mellitus (IDDM) were examined in a cross-sectional study. The main outcome measures were serum total renin concentration and urinary albumin excretion rate.', 'The total renin concentrations in serum were significantly (P < 0.05) higher in 12 patients with microalbuminuria than in 43 patients without albuminuria, but this difference was significant only in men. There was a significant but weak positive correlation between urinary albumin excretion rate and serum total renin concentration in all patients (r = 0.412, P < 0.05, n = 55), but the sensitivity of high serum concentrations of total renin in detecting incipient nephropathy was low (17%). In the study group, two of the three patients suffering from proliferative retinopathy had the highest total renin concentrations in serum.'] Is elevated serum total renin insensitive in detecting incipient diabetic nephropathy?