The need for ethnic-specific reference values of lung function variables (LFs) is acknowledged. Their estimation requires expensive and laborious examinations, and therefore additional use of results in physiology and epidemiology would be profitable. To this end, we proposed a form of prediction equations with physiologically interpretable coefficients: a baseline, the onset age (A0) and rate (S) of LF decline, and a height coefficient. The form was tested with data from healthy, nonsmoking Poles aged 18-85 yr (1,120 men, 1,625 women) who performed spirometry maneuvers according to American Thoracic Society criteria. The values of all the coefficients (also A0) for several LFs were determined with regression of LF on patient's age and deviation of patient's height from the mean height in the year group of this patient. S values for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow, and maximal expiratory flow at 75% of FVC (MEF75) were very similar in both sexes (1.03+/-0.07%/yr). FEV1/FVC declines four to five times slower. S for MEF25 appeared age dependent. A0 was smallest (28-32 yr) for MEF25 and FEV1. About 50% of each age subgroup (18-40, 41-60, 61-85 yr) exhibited LFs below the mean, and 4-6% were below the 5th percentile lower limits of normal, and thus the form of equations proposed in the paper appeared appropriate for spirometry. Additionally, if this form is accepted, epidemiological and physiological comparison of different LFs and populations will be possible by means of direct comparison of the equation coefficients.