Our objective was to assess mean transit time (MTT) and initial uptake, both parameters derived from the renal retention function (RRF), in the study of renal function in patients with diabetic nephropathy. We studied 25 patients, 7 with type I diabetes mellitus and 18 with type II diabetes mellitus, all of whom fulfilled the criteria for diabetic nephropathy with proteinuria and/or retinopathy. We found a statistically significant correlation between initial uptake and the other biochemical and renographic parameters studied except proteinuria: serum creatinine (r = 0.66, P < 0.002), creatinine clearance (r = 0.61, P < 0.003), glomerular filtration rate (r = 0.74, P < 0.003) and effective renal plasma flow (r = 0.66, P < 0.003). The other renographic parameters studied (maximal activity of the conventional renogram and MTT of the deconvoluted renogram) did not show any correlation. Initial uptake is a semi-quantitative renographic parameter that can provide complementary information to biochemical data and it may be useful in the management of diabetic nephropathy, especially in patients with high serum creatinine or creatinine clearance.