Reference values of the maximal expiratory flow-volume curve for the adult GDR's population have been ascertained by a co-operative study of 5 lung function laboratories. We analysed measurements in 1,004 healthy subjects aged 16 to 69 years (728 males and 276 females). Prediction equations for the maximal expiratory flow rates, several time constants of lung mechanics and screening parameters of ventilatory inhomogeneity have been calculated by means of the multiple linear regression analysis. Our reference values are in good accordance with SEPCR summary equations. It is recommended to subtract from or add to the predicted values 1.64 standard deviations and to consider abnormal all values beyond this limit.