Spirometry was performed on 614 female subjects ranging in age from 13 to 69 years and comprising all the main races in Malaysia. They were divided into six age categories. Mean forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) were 2.51 +/- 0.02 and 2.31 +/- 0.02l, respectively. Both FVC and FEV1 correlated negatively with age. Regression analysis revealed an age-related decline in FVC of 220 ml per decade of life. Multiple stepwise regression of the data for the prediction of an individual's FVC above the age of 20 years gave an equation: FVC(l) = 0.0312 (height)-0.022 (age)-1.64. Predicted FVC values derived from equations based on other populations were considerably higher than the observed mean in this study. Our study, therefore, reemphasizes the need to be cautious when applying formulae derived from one population to another. Grossly erroneous conclusions may be reached unless predicted equations for lung-function tests for a given population group are derived from studies based on the same population group.