Renal hemodynamics in newly presenting non-insulin dependent diabetes mellitus. Little information is available regarding renal hemodynamics in non-insulin dependent diabetics (NIDDMs), despite their numerical significance to renal support programs. Therefore, simultaneous determination of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) (expressed to 1.73 m2 surface area) was performed in 110 newly presenting normotensive NIDDMs [mean (SD) age: 52.5 (10.1) years] and compared with 32 normal subjects of similar age range [age: 52.2 (11.3) years]. Mean (SD) GFR, ERPF and filtration fraction (FF) for the NIDDMs were: 117 (22) ml/min (range: 74 to 178), 534 (123) ml/min and 22.4 (3.0)%, and for the normals: 95 (12) ml/min (range: 75 to 119), 472 (70) ml/min and 20.2 (2.2%), respectively. As a group, NIDDMs demonstrated significantly greater GFR (P < 0.001), ERPF (P < 0.005) and FF (P < 0.001). GFR values above 140 ml/min were observed in 16% of the NIDDMs, while 45% had GFRs in excess of mean ± 2 SD of the normals. NIDDMs demonstrated a positive relationship for GFR with ERPF (P < 0.001) and an inverse association for both GFR and ERPF with age (P < 0.001). Multivariable regression analysis revealed ERPF as the strongest explanatory variable for GFR in the NIDDMs (P < 0.001), followed by age (P < 0.01). Significant contributions to the regression analysis were not observed for body mass index, systolic or diastolic blood pressures, glycosylated hemoglobin nor fasting levels of plasma glucose, cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides. Urinary albumin excretion rates were not correlated with GFR, ERPF or FF. Microalbuminuria was detected in 7% of the NIDDMs in this study. We conclude that newly presenting NIDDMs demonstrate a wide range of GFR, unrelated to blood pressure, prevailing glycamie parameters or lipid levels. GFR, ERPF and filtration fraction are greater for the NIDDMs than the normals, and hyperfiltration is present in a significant proportion of the NIDDMs.