The kidney is the main organ involved in drugs elimination and thereby is particularly liable to their toxic effect. The determination of renal function is thus of importance, before and during treatment with a potentially nephrotoxic drug or during trial of new drugs. In this general review, the main methods to measure renal function are briefly analysed. They consist either of simple dosages in blood and urine which allow to roughly evaluate renal functional value and its variations, or more sophisticated investigations which allow a more precise analysis of various nephron functions: glomerular filtration rate and renal plasma flow with measurement of clearances of exogenous markers, determination of basal or maximal tubular activities. The interest of these specific tests is illustrated by the results of a study performed in patients receiving streptozotocin, an antineoplastic nephrotoxic drug. In conclusion, nephrotoxicity of drugs may be in most cases prevented owing to an accurate knowledge of their pharmacokinetics and of risk factors inherent in patients, and to survey of renal function with suitable methods which may lead to modify drug dosage and/or to choose a therapy considering the own evolution of the disease and the possible occurrence of irreversible renal impairment.