Flow-volume and spirometric parameters obtained in a randomly selected population were examined with regard to their sensitivity in detecting abnormalities among persons who smoked and/or had respiratory symptoms. Data obtained from subjects who were totally free of cardiorespiratory symptoms and who had never smoked cigarettes were used to develop "normal" prediction equations. Using as normal limits the per cent of predicted value above which 95% of these "normal" subjects fell, maximal expiratory flow at 75% of the expired vital capacity (Vmax75) detected the greatest proportion of abnormalities in the remainder of the population. When examined according to age, however, Vmax75 was most sensitive in older subjects, whereas 1-sec forced expiratory volume was superior in younger subjects. There was a slight tendency for Vmax75 to be affected in subjects with reactive airway syndromes and for the 1-sec forced expiratory volume to be affected in heavy smokers or subjects with chronic productive cough. If one parameter was markedly abnormal, the entire flow-volume curve was likely to be affected, but concordance of the parameters examined was not complete. For the latter reason, considerable caution must be exercised in attempting to use multiple parameters in defining abnormality, unless one applies more stringent criteria for abnormality.