Forced expiratory volumes and flows were measured in 251 healthy nonsmoking men and women using techniques and equipment that meet American Thoracic Society (ATS) recommendations. Linear regression equations using height and age alone predict spirometric parameters as well as more complex equations using additional variables. Single values for 95% confidence intervals are acceptable and should replace the commonly used method of subtracting 20% to determine the lower limit of normal for a predicted value. Predicted values were produced for forced vital capacity and 1s forced expiratory volume that were almost identical to those predicted by the Morris study when the data from the latter study were modified to be compatible with the back extrapolation technique recommended by the ATS. The Morris study was performed at sea level in rural subjects; the present study performed at an altitude of 1,400 m in urban sujects. Either the present study or the Morris study modified to back extrapolation, could be recommended for predicting normal values.