The relationships of lung functions to maximal respiratory pressure relative to the role of other recognized determinants (height, weight, age, and smoking status) were examined in 924 healthy Caucasian urban residents, 369 males 15 to 35 yr of age and 555 females 13 to 35 yr of age. In subjects no longer thought to be growing in stature, height was the main determinant of most functions. After height, respiratory pressures were the main determinant of forced vital capacity (FVC), forced expiratory volume in one second (FEV), and peak flow in men and women, with weight also an important determinant in women. Age had no consistent effect, and, although functions in smokers were lower than in nonsmokers for several tests, the effects were only significant for FEV and forced expiratory flow during the middle half of the FVC in women. These findings indicate that, if required, between-subject variation in this age group can be reduced by taking into account the relatively simple measurement of maximal inspiratory and expiratory pressures.