A method is described for the semi-automated measurement of inulin concentrations in serum and urine in the presence of glucose. The concentration of glucose is measured simultaneously and is used to correct for almost all "inulin-like" interferences. The inulin standard curve is linear over a wide range (5-2500 mg/l). Between-run precision is < 6% and recovery from spiked sera is 98%. This method offers the possibility of measuring glomerular filtration rate in patients with varying glucose concentrations (e.g. diabetics).