Single breath pulmonary function tests of the forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) type require adjustments for age and height before the extent of their deviation from normal standards can be assessed. Many regression equations have been proposed in the literature. The Committee on Rating of Mental and Physical Impairment (1965) has provided tables of normal values of FEV1 and FVC for adults by sex, age, and height. These recommended standards were adapted from a study in the United States (Kory, Callahan, Boren, and Syner, 1961 non-bronchitic subjects for the calculation of expected values of FEV1, FVC, and FEV1 % (defined as FEV1 x 100) FVC The study showed that both age and height were significant predictors for estimating FEV1 and FVC, but that age alone was of importance for FEV1 %. All the three ventilatory functions decreased with age, and within age groups FEV1 and FVC increased with height. The within age regression coefficients of FEV1 and FVC on height were, however, significantly non-parallel, and their slopes decreased appreciably with age. In a later part of this study (Lowe, Campbell, and Khosla, 1970) it was reported that the groups of smokers not only had lower values of FEV1 at each age group than the nonsmokers, but their decline of FEV1 with age was also steeper.These results show that the overall multiple regression coefficient of FEV1 on age in any particular study is likely to be influenced by the smoking habits or the health condition of the group, and the regression coefficient of FEV1 on height could be affected by the age distribution. It is, therefore, not surprising that the regression relationships reported in the literature differ in their regression